Coated metal material capable of being welded which is excellent in corrosion resistance of worked zone

ABSTRACT

A weldable coated metal material excellent in the corrosion resistance of the formed part, comprising a metal sheet having formed on at least one surface thereof a coat layer containing electrically conducting particles, wherein the number distribution of the electrically conducting particle has a mode value in the particle size range from 0.05 to 1.0 μm and the total content of electrically conducting particles in the coat layer is from 15 to 60 vol %.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a metal sheet, having formed thereon acoat layer containing electrically conducting particles, which is usedfor automobiles, home appliances, OA devices, civil engineering buildingmaterials and the like. Particularly, the present invention relates to aweldable coated metal material excellent in the corrosion resistance ofthe formed part and, more specifically, a coated metal material notsusceptible to the generation of corrosive perforation in the portionformed by press forming even when formed through press forming andelectric resistance welding and used in a corrosive environment withoutapplying rust-preventive coating. The present invention also relates toa rust-preventive steel sheet having excellent corrosion resistance andexhibiting both good resistance weldability and good press formability,which is used as a material particularly for the fuel tank ofautomobiles.

BACKGROUND ART

In order to prevent a metal material from the environmental corrosionduring use, application of various coating materials has been heretoforeemployed. The coat layer formed on the metal sheet usually uses anelectrically non-conducting resin as the binder and therefore, thislayer has no electric conductivity and can be hardly welded andearth-grounded. To solve this problem, a technique of forming a coatlayer containing electrically conducting particles on a metal sheet toimpart electric conductivity and thereby enable welding orearth-grounding has been proposed.

For example, Japanese Unexamined Patent Publication (Kokai) No.09-234820 discloses a technique of imparting weldability by subjectingthe metal sheet to coating with a resin using iron phosphide as theelectrically conducting particles. In this method, the amount of theelectrically conducting particles is specified to be 20 to 45 mass % andthe weldability is ensured by controlling the amount to this range. Asfor the particle size, it is stated that the particles preferably havean average particle size of 20 μm or less.

Japanese Unexamined Patent Publication (Kokai) No. 07-314601 discloses atechnique of imparting an earthing property by using nickel-basedparticles as the electrically conducting particles. In this method, theaverage value and the maximum value are specified with respect to theparticle size of the electrically conducting particles and it is statedthat the matter of importance for ensuring electrical conductivity is toadd, in the case of a scale-like particle, from 11 to 200 parts of theelectrically conducting particles having a long diameter of 100 μm as amaximum and 15 μm on average and in the case of a chain-like particle,10 parts or less of the electrically conducting particles having amaximum particle size of 44 μm and an average particle size of 2.5 μm.

Also, in Japanese Unexamined Patent Publication (Kokai) No. 01-60668,the ratio of the average particle size of metal-based particle to thethickness of coating film is specified for imparting the electricalconductivity and it is stated that when the average particle size isfrom 0.5 to 3 times the film thickness, electric conductivity can beensured. The particle size is not particularly described but inExamples, a particle having an average particle size of 7.5 to 25 μm isused.

Recently, Japanese Unexamined Patent Publication (Kokai) No. 2002-172363has proposed a technique of coating an organic resin film containingfrom 10 to 70 mass % of ferrosilicon having a particle size of 0.5 to 10μm on a zinc-plated steel sheet to a thickness of 2.5 to 8 μm to obtaina surface-treated steel sheet having excellent weldability.

The techniques disclosed in these publications are satisfied in terms ofimparting electric conductivity to the coat layer and thereby ensuringweldability or earth property as a coated metal sheet, but are stillinsufficient from the aspect of obtaining satisfactory formability andcorrosion resistance as well as stable weldability and an earthingproperty. One of the causes therefor is in that only the concept ofaverage or maximum particle size is used in designing the particle sizeof the particle but the particle size distribution is not taken intoconsideration.

Japanese Unexamined Patent Publication (Kokai) Nos. 09-234820 and2002-172363 supra disclose that a rust-preventive pigment is added forthe purpose of enhancing the corrosion resistance. However, when arust-preventive pigment is added in addition to the electricallyconducting pigment, the electric conductivity or formability decreasesand therefore, if possible, the addition of a rust-preventive pigmentmust be minimized. Japanese Unexamined Patent Publication (Kokai) No.2002-172363 also discloses that when a zinc alloy-plated steel sheet isused for the underlying plated steel sheet, a coated steel sheet havingmore excellent corrosion resistance can be obtained. However, a changein the kind of plating may cause increase in the cost or may sacrificeother performances and therefore, it is demanded to obtain highcorrosion resistance or formability independently of the kind of theunderlying steel sheet.

In order to solve these problems, a first object of the presentinvention is to provide a coated metal sheet excellent in electricconductivity (for example, weldability and an earthing property),corrosion resistance and formability.

In a metal-made part for the outer panel of automobiles, the joinedportion or folded hem portion on the inner surface of a hollow partprone to severe corrosion is coated by electrodeposition painting and/orapplied with a rust-preventive subsidiary material such as sealer,adhesive and wax, whereby the corrosion resistance is ensured in manycases. On the other hand, studies are being made to reduce theproduction cost of an automobile by omitting or decreasing the paintingon the inner surface of an automobile part or the rust-preventivetreatment with sealer-wax or the like, which is performed for thepurpose of rust prevention, and various coated steel sheets have beenheretofore proposed. For example, Japanese Unexamined Patent Publication(Kokai) No. 55-17508 discloses a technique of forming a zinc-containingcoating film on a steel sheet surface. Also, a steel sheet capable ofensuring rust perforation resistance even when electrodepositionpainting or rust-preventive subsidiary material is not applied has beenproposed and, for example, Japanese Unexamined Patent Publication(Kokai) Nos. 9-23480, 10-128906 and 11-5269 disclose a steel sheet wherean electrically conducting resin coat layer is formed on a steel sheetsurface. As for the constitution thereof in general, an organic filmcontaining an electrically conducting or rust-preventive pigment iscoated on a plated steel sheet through an undercoating layer.

However, when the steel sheet coated with such an organic film is formedas an automobile part through severe drawing or bending of pressforming, the corrosion resistance in the formed part may decrease. Oneof the reasons therefor is because the film cannot follow thedeformation of steel sheet and this causes cracking or separation of thefilm. Also, when the film is made thick so as to ensure sufficientlyhigh corrosion resistance, this causes problems that welding and, inturn, stable production become difficult and the cost increases.Accordingly, conventional coated steel sheets decrease in the corrosionresistance or must receive a repair coating.

A second object of the present invention is to provide a weldable coatedmetal material in which, even when the steel sheet is greatly deformedby the forming under severe conditions, sufficiently high corrosionresistance can be ensured in the formed part.

In fuel tanks of automobiles, excellent formability (deep-drawingproperty) is required because the fuel tank has a complicated form inmany cases. Also, the fuel tank is an important safety part of anautomobile and therefore, it is essential that the material usedtherefor generates no corrosion product giving rise to filter clogging,is freed from corrosive perforation, and can be easily and stablywelded. As for the material having these various properties, a lead-tinbased alloy-plated steel sheet (see, Japanese Examined PatentPublication (Kokoku) No. 57-61833) has been heretofore widely used as amaterial for the fuel tank of automobiles. This material has a stablechemical property against gasoline, excellent press formability byvirtue of high lubricity of the plating, and also excellent resistanceweldability such as spot welding and seam welding. However, in view ofenvironmental impact, materials not using lead are demanded and thereare disclosed techniques such as tin-based alloy-plated steel sheet(see, for example, Japanese Unexamined Patent Publication (Kokai) No.8-269733), aluminum-based alloy-plated steel sheet (see, for example,Japanese Unexamined Patent Publication (Kokai) No. 9-156027), metal- ororganic film-coated zinc-based alloy-plated steel sheet (see, forexample, Japanese Unexamined Patent Publication (Kokai) No. 08-296834).

In recent years, enhancement of the rust-preventive fuel tank to anextent of assuring no perforation over 15 years is demanded in NorthAmerica and with this requirement, there arises a problem that corrosionresistance by conventional techniques is insufficient. When a tank isproduced through forming and welding and then applied with multi-plycoating, long-term rust prevention can be achieved, but in this case, aproblem of incurring a great increase in the cost arises. Also, forexample, Kokai No. 6-306637 discloses a technique of applying a metalpowder-containing organic film to an aluminum-based alloy-plated steelsheet, but this method has a problem in that, when the steel sheet isshaped through severe drawing or bending of press forming, the filmcannot follow the deformation of steel sheet and this may cause crackingor separation of the plating layer or the film to decrease the corrosionresistance of the formed part or in that when the film is made thick soas to ensure sufficiently high corrosion resistance, the welding and inturn the stable production become difficult and the cost increases.Furthermore, Japanese Unexamined Patent Publication (Kokoku) No. 3-25349discloses a technique of coating a zinc-plated steel sheet with anorganic film containing various metal powers, but the zinc-based platinghas a fear of causing filter clogging due to generation of corrosionproduct ascribable to an organic acid and coagulated water produced bygasoline degradation particularly in the portion subjected to severeforming. In addition, as the outer surface is also required to have highcorrosion resistance, an organic coating film having a larger thicknessmust be applied to both the inner surface and the outer surface and thismay cause problems that the welding and, in turn, the stable production,become difficult and the cost increases.

A third object of the present invention is to overcome theabove-described problems in the performance and production and provide arust-preventive steel sheet capable of realizing, as a fuel tank, highinner surface corrosion resistance and exhibiting good formability andstable weldability.

DISCLOSURE OF THE INVENTION

One technical point of the present invention is in the finding that whenthe particle size of the electrically conducting particle formed on ametal sheet is designed by taking account of not only the “averageparticle size” proposed, for example, in Kokai Nos. 07-314601 and2000-319790 but also the size distribution, the electric conductivity,corrosion resistance and formability all can be satisfied at the sametime. Another technical point is in the finding that although theelectric conductivity is conventionally ensured by adding electricallyconducting particles having a relatively large average particle size,for example, an average particle size larger than a certain level basedon the thickness of coating film as described in Kokai No. 01-60668,when electrically conducting particles having a small particle size areused, this rather yields stable electric conductivity and also givesgood effect on the corrosion resistance and formability.

Also, in thinking that it is necessary for ensuring corrosion resistanceparticularly in the formed part that the organic film of a coated steelsheet properly follows the deformation of the underlying steel material,the present inventors have made investigations on the components in theresin for the organic film, the kind of pigment added and the blendingratio thereof. As a result, it has been found that when an organic filmcontaining electrically conducting particles comprising (1) a resinhaving a urethane bond and (2) (i) a metal and/or (ii) an alloy orcompound of a typical metal, transition metal or semimetal element isapplied to the entire or partial surface of a metal material, even ifthe metal material is greatly deformed by the forming under severeconditions, sufficiently high corrosion resistance can be ensured alsoin the formed part; and that when a certain kind of silicon compound isfurther used as the electrically conducting particle or arust-preventive pigment is further added, a more enhanced corrosionresistance can be obtained. The present invention has been accomplishedbased on these findings.

Furthermore, the present inventors have made various investigations on arust-preventive steel sheet for tanks, having excellent corrosionresistance and also being excellent in weldability and formability and,as a result, it has been found that when a film mainly comprising anorganic resin containing an electrically conducting pigment is formed onat least one surface of a surface-treated steel sheet and when the filmhas a thickness of 5 to 30 μm and a surface roughness of 0.3 to 2.5 μmas the average roughness from center line of surface roughness (Ra) or20 μm or less as the maximum height of surface roughness (Rmax) and/orthe peak count of surface texture (Pc) of surface texture is controlledto from 10 to 200 peaks per 10-mm length with a count level of 0.3 μm,good press formability and stabilized continuous weldability can beobtained and the corrosion resistance is also satisfied. It has beenalso found that when an tin or tin-based alloy coat layer is formed on asurface of a steel sheet and after applying an undercoating film to onesurface or both surfaces of the steel sheet, an organic film containingan electrically conducting pigment is further formed on one surface orboth surfaces of the steel sheet, the above-described problem in thelong-term corrosion resistance can be solved and at the same time,excellent properties, for a fuel tank, appear.

Specifically, the present invention provides the following.

(1) A weldable coated metal material excellent in the corrosionresistance of the formed part, comprising a metal sheet having formed,on at least one surface thereof, a coat layer containing electricallyconducting particles, wherein the number distribution of theelectrically conducting particles have a mode value in the particle sizerange from 0.05 to 1.0 μm and the total content of electricallyconducting particles in the coat layer is from 15 to 60 vol %.

(2) The coated metal material as described in (1) above, wherein thenumber of particles at the mode value in the number distribution of theelectrically conducting particles occupies 5% or more in the number ofall electrically conducting particles.

(3) The coated metal material as described in (1) or (2) above, whereinthe volume distribution in relation to particle size of the electricallyconducting particles has a mode value of 2 to 20 μm.

(4) The coated metal material as described in any one of (1) to (3)above, wherein the average thickness of the coat layer is from 2 to 20μm.

(5) The coated metal material as described in any one of (1) to (4)above, wherein the maximum particle size of the electrically conductingparticles is 25 μm or less.

(6) A coated metal material excellent in electric conductivity,corrosion resistance and formability, comprising a metal sheet havingformed on at least one surface thereof a coat layer containingelectrically conducting particles, wherein assuming that the mode valuein the number distribution in relation to particle size of theelectrically conducting particles is Mn, the mode value in the volumedistribution in relation to particle size of the electrically conductingparticle is Mv and the thickness of the coat layer is H,

-   -   H/10≦Mv≦10H    -   5Mn≦H≦200Mn    -   12≦Mv/Mn≦50        and at the same time, the content of the electrically conducting        particle in the coat layer is from 15 to 60 vol %.

(7) The coated metal material as described in (6) above, wherein Mn isfrom 0.05 to 1.5 μm and Mv is from 2 to 30 μm.

(8) The coated metal material as described in (6) or (7) above, whereinthe thickness H of the coat layer is from 2 to 20 μm.

(9) The coated metal material as described in any one of (6) to (8)above, wherein the maximum particle size of the electrically conductingparticle is 35 μm or less.

(10) The coated metal material as described in any one of (1) to (9)above, wherein the electrically conducting particles comprise (i) ametal and/or (ii) an alloy or compound of a typical metal, transitionmetal or semimetal element.

(11) The coated metal material as described in any one of (1) to (10)above, wherein the electrically conducting particles are ferrosilicon.

(12) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (6) to (11)above, wherein the binder component in the coat layer mainly comprises athermoplastic resin.

(13) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (6) to (12)above, wherein the coat layer contains 20 vol % or less in total of arust-preventive pigment and/or silica.

(14) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (1) to (13)above, wherein the binder component in the coat layer mainly comprises aurethane bond-containing resin.

(15) A weldable coated metal material excellent in the corrosionresistance of the formed part, which is a coated metal material having acoat layer containing electrically conducting particles, wherein thebinder component in the coat layer is a resin system mainly comprising aurethane bond-containing resin and the urethane bond-containing resin isan organic resin produced from a raw material film-forming resincontaining (a) a polyester polyol having at least three functionalgroups and (b) a blocked organic polyisocyanate or a blocked product ofa prepolymer having an NCO group at the end obtained by the reaction ofan organic polyisocyanate with an active hydrogen compound.

(16) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in (15) above, wherein theurethane bond-containing resin is an organic resin produced from a rawmaterial film-forming resin containing (a) a polyester polyol having atleast three functional groups, (b) a blocked organic polyisocyanate or ablocked product of a prepolymer having an NCO group at the end obtainedby the reaction of an organic polyisocyanate with an active hydrogencompound, and (c) an epoxy resin having at least one secondary hydroxylgroup or an adduct thereof.

(17) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in (15) or (16) above,wherein the organic film further comprises a rust-preventive pigment.

(18) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (15) to (17)above, wherein the electrically conducting particles in the organic filmare an alloy or compound containing 50 mass % or more of silicon or acomposite material thereof.

(19) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (15) to (18)above, wherein the electrically conducting particles in the organic filmare ferrosilicon containing 70 mass % or more of silicon.

(20) The coated metal sheet as described in any one of (17) to (19)above, wherein the coat layer contains 20 vol % or less in total of therust-preventive pigment and/or silica.

(21) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (1) to (20)above, wherein an organic resin film containing electrically conductingparticle is formed as the coat layer on at least one surface of asurface-treated steel sheet and the surface roughness of the organicfilm is from 0.3 to 2.5 μm as the average roughness from center line ofsurface roughness Ra.

(22) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in (21) above, wherein thecontent of the electrically conducting pigment in the organic film isfrom 5 to 50 vol % in terms of the solid content.

(23) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in (20) or (21) above,wherein the electrically conducting pigment comprises one or more memberselected from the group consisting of stainless steel, zinc, aluminum,nickel, ferrosilicon and iron phosphide.

(24) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (21) to (23)above, wherein one electrically conducting pigment is an alloy orcompound containing 40 mass % or more of silicon or a composite materialthereof.

(25) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (21) to (24)above, wherein the organic film further contains from 1 to 40 vol %, interms of the solid content, of a rust-preventive pigment and the sum ofthe electrically conducting pigment and the rust-preventive pigment isfrom 5 to 70 vol % in terms of the solid content.

(26) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (21) to (25)above, wherein the surface roughness of the organic film is 20 μm orless as the maximum height Rmax.

(27) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (21) to (26)above, wherein the surface texture of the organic film has a peak countPc of 10 to 200 peaks per 10-mm length with a count level of 0.3 μm.

(28) A weldable coated metal material excellent in the corrosionresistance of the formed part, obtained by forming a tin or tin-basedalloy coat layer on a surface of a steel sheet, applying an undercoatingfilm to a coverage of 10 to 1,000 mg/m² on one surface or both surfacesof the steel sheet, and further forming an organic film containing anelectrically conducting pigment to a thickness of 1.0 to 20 μm on onesurface or both surfaces of the steel sheet.

(29) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in (28) above, wherein theorganic film is a resin system mainly comprising a urethanebond-containing resin and the urethane bond-containing resin is anorganic resin produced from a raw material film-forming resin containing(a) a polyester polyol having at least three functional groups and (b) ablocked organic polyisocyanate or a blocked product of a prepolymerhaving an NCO group (an isocianate group: —N═C═O) at the end obtained bythe reaction of an organic polyisocyanate with an active hydrogencompound.

(30) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in (29) above, wherein theurethane bond-containing resin is an organic resin produced from a rawmaterial film-forming resin further containing, in addition to (a) and(b), (c) an epoxy resin having at least one secondary hydroxyl group oran adduct thereof.

(31) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (28) to (30)above, wherein the organic film comprises from 1 to 50 vol % of anelectrically conducting pigment and from 5 to 40 vol % of arust-preventive pigment and the electrically conducting pigment andrust-preventive pigment account for from 5 to 70 vol % of the entirecoating film.

(32) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (28) to (31)above, wherein the electrically conducting pigment comprises one or moremember selected from the group consisting of stainless steel, zinc,aluminum, nickel, ferrosilicon and iron phosphide.

(33) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in any one of (1) to (32)above, which comprises an undercoating film between the organic film andthe surface-treated steel sheet.

(34) The weldable coated metal material excellent in the corrosionresistance of the formed part as described in (33) above, wherein thecoverage of the undercoating film is from 10 to 1,000 mg/m².

In the above, (1), (6), (15), (21) and (28) each is an independentaspect of the present invention having a characteristic feature, butthese aspects can be combined to have characteristic features ofrespective aspects and depending on the case, a synergistic effect canbe provided. Such combinations are belonging to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an example of a fuel tank.

MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention are described in detail below.

In the present invention, formation of a coat layer containingelectrically conducting particles on at least one surface of a metalsheet is essential and with respect to the particle size of theelectrically conducting particles, the mode value in the numberdistribution in relation to particle size must be from 0.05 to 1.0 μm.

The particle size has a distribution but in conventional techniques, asimple concept of “average particle size” has been used. The averageparticle size is simply determined by an arithmetic calculation ofparticle sizes of individual particles. However, the present inventorshave realized that the mere average of particle sizes is not importantbut the particle size distribution and particularly, which particle sizeis possessed by many particles, greatly affects the electricconductivity (weldability or earth property), corrosion resistance andformability of the entire coated metal sheet. The particle size ofparticle is measured, the number of particles having the measuredparticle size is counted, the number distribution in relation toparticle size is examined, and the particle size having a largest numberof particles (mode value) is determined. When the mode value is from0.05 to 1.0 μm, each performance is high and a good balance is obtained.In examining the number distribution, the data are preferably sampled bysetting the range in the measurement of the number of particles havingthe particle size to 0.05 μm (0.025 μm before and after the particlesize indicated value). In the coating material (liquid) state, theparticle size distribution can be easily examined by a size distributionmeter. In the case of a coating film state, a secondary electron imageof the cross section of the coating film is photographed and the actualparticle size of the particle is measured. In the case where theparticle is not spherical, the long diameter is defined as the particlesize of the particle. When the particle size distribution is a normaldistribution, the average particle size agrees with the mode value asused in the present invention but, in fact, when the particle is kept inthe ground state or when the particles are dispersed after a coatingmaterial state is produced, a larger number of particles having a largerparticle size remain to give a tail on the large particle size side andthe average particle size does not agree with the mode value.

If the mode value is less than 0.05 μm, the process of pulverizing theparticle takes a long time or secondary aggregation of particles oftenoccurs and this is not practical. Also, the electric conductivitydecreases. On the other hand, if the mode value exceeds 1.0 μm, theproportion of large particles increases to cause reduction in thecorrosion resistance and formability. The mode value is more preferablyfrom 0.05 to 0.5 μm and with this range, the electric conductivity,corrosion resistance and formability become particularly good.

When the number of particles having a particle size at the mode valueaccounts for 5% or more of the number of all particles, particularlygood performances can be obtained. This is preferably 7% or more.

The particle size of the electrically conducting particle, which issmall as compared with conventional inventions, is also onecharacteristic feature of the present invention. The general thinking inconventional techniques is such that the particle size is made largerthan a certain level based on the thickness of coating film to allow theparticles to penetrate through the coating film or the coating film ispartially ruptured due to pressure of the electrode at the welding toput the electrically conducting particles into contact with theelectrode, whereby the electric conductivity is ensured. In this case,when the thickness becomes large, the particle size of the particle mustbe also enlarged for ensuring the electric conductivity, and thistechnique is substantially effective only when the coating thickness issmall. The present invention is based on the thinking that a relativelylarge amount of particles having a small particle size are contained inthe coat layer and the electrification path is thereby stably ensured.Therefore, the entire particle is made small and for ensuring the amountof particles having a small particle size, the mode value is used as themeasure. By this constitution, the electric conductivity can be ensuredeven when the film thickness becomes large and the particle size issmall. Furthermore, a more preferred film can be specified by specifyingthe relationship between the particle size and the film thickness.

The present inventors have further realized that the mode value for thevolume distribution every each particle size of the electricallyconducting particles is also important. Insofar as the mode value in thenumber distribution of the particle size is in the above-describedrange, the electric conductivity, corrosion resistance and formabilitybecome good, but furthermore, when the mode value for the volumedistribution is in the range from 2 to 20 μm, the performances inparticular are enhanced. This value is determined by measuring volumesof individual particles every each particle size and calculating theratio of the total volume of particles having that particle size to theentire volume of all particles. The particle size having a largest ratiois defined here as the mode value for the volume distribution every eachparticle size. This mode value is an index more strongly showing theeffect of particles having a large particle size and when the number oflarge particles is large, this value becomes outstandingly large. Evenwith the same mode value for the number distribution, when the largeparticle size side has a large distribution, this value becomes large.If the mode value for the volume distribution is high, the weldabilityin particular is liable to decrease. The decrease in weldability as usedherein means reduction in the continuous dotting property and easygeneration of cracking in the metal sheet of the welded part.

If this mode value exceeds 20 μm, the weldability, particularlycontinuous dotting property, decreases and the formability or corrosionresistance also decreases. In order to render this mode value to be 2 μmor less, the particle must be made small, requiring much labor, and thisis unprofitable. At the same time, if the content of the electricallyconducting particle is small, the electric conductivity decreases. Asdescribed above, if the mode value is high, the continuous weldabilityin particular is liable to decrease. The reason therefor is presumed tobe as follows. If the mode value for the volume distribution becomeslarge, the coat layer is more increased in the unevenness and only theprotruded part of the coat layer is easily contacted with the electrodefor welding to cause unstable electrification, as a result, generationof dust increases and the electrode is readily fouled. Furthermore, dueto local generation of heat, the form of the nugget is worsened and thewelding intensity becomes unstable. Since hard electrically conductingparticles are present in the protruded part, the coat layer is notcompressed by the pressure between electrodes and the electrification isensured only by the one electrically conducting particle. In such anelectrification form, the electric current is liable to concentrate atone point and, in turn, the generation of heat is liable to concentrateat that portion. Due to the effect of this heat, cracking of the metalsheet itself is readily generated in the welded part and in the vicinitythereof. On the other hand, when the mode value in the volumedistribution is 20 μm or less or when the relationship between theparticle size distribution and the film thickness is within the rangespecified in the present invention, the number of particles having alarge particle size is decreased and this gives a smoother coat layersurface, as a result, the electrode can be contacted with a larger areaof the coat layer, stable electrification can be obtained and a nuggetin a normal form can be easily formed. Also, by virtue of the absence oflarge particles, the coat layer is slightly compressed by the pressurebetween electrodes, whereby electrification among electricallyconducting particles is more easily ensured and the electricconductivity is enhanced. Furthermore, as the electric current does notconcentrate at one point, the phenomenon that the metal sheet in thewelded part or in the vicinity of the welded part is cracked can beprevented.

Within the range specified in the present invention, the formability isalso enhanced than ever before. The reason therefor is because due toabsence of excessively large particles, the particles less exfoliate atthe exfoliate shaping and also the cracking of the coating film at theshaping, which takes place in many cases in the vicinity of theinterface between the particles and the binder component, is reduced. Inaddition, the coating film surface is free from excessive unevenness, sothat the coating film surface can have good slidability and theappearance and corrosion resistance after a draw-bead test or the likecan also become better. The same applies to the draw-forming.

By virtue of good formability and no exfoliation or damage to a part ofthe coating film, the corrosion resistance is also enhanced.Particularly, in the case of using a particle having a rust-preventiveeffect, such as ferrosilicon, the increase in the surface area of theparticle also provides an effect of enhancing the corrosion resistance.

In the present invention, the particle size distribution of theelectrically conducting particles can be varied by a known method suchas mechanical grinding or classification. The electrically conductingparticle may be mixed in a binder for forming the coat layer afteradjusting the size distribution to a specific range and then dispersedin the binder layer by a method of unchanging the size distribution,such as almost shearless stirring, or may be mixed in the binder andthen dispersed under the conditions of causing the particle to beground. The order of grinding and dispersion is not particularlylimited.

The mode value in the volume distribution may be measured by acommercially available size distribution meter or in the above-describedmethod of determining the particle size distribution by observing thecross section of the coat layer, may be determined from the particlesize assuming that the particle is a sphere.

In the present invention, it is essential that the total content ofelectrically conducting particles in the coat layer is from 15 to 60 vol%. If the content is less than 15 vol %, insufficient electricconductivity results, whereas if it exceeds 60 vol %, the formabilitydecreases. The total content is preferably from 20 to 35 vol %.

In the present invention, the film thickness is substantially notlimited, but when the film thickness is from 2 to 20 μm, the electricconductivity, corrosion resistance and formability in particular areenhanced and this is preferred. If the film thickness is less than 2 μm,the corrosion resistance decreases, whereas if it exceeds 20 μm, this isdisadvantageous in view of profitability and also, the formability orearth property decreases. The coat layer may not be a single layer butmay comprise multiple layers. If desired, another layer may be formed onor below the coat layer of the present invention. For example, anundercoating layer may be formed as the lower layer or a layer forimparting scratch resistance or other functions may be formed as theupper layer.

When the maximum particle size of the electrically conducting particleis 25 μm or less, the formability in particular is enhanced and this ispreferred. Independently of the film thickness, if the maximum particlesize is larger than this range, the coat layer is readily cracked whenformed. Particularly, in the case where the film thickness is from 2 to20 μm, when the maximum particle size of the electrically conductingparticles is 25 μm or less, the electric conductivity, corrosionresistance and formability become best.

In the present invention, as for the particle size distribution of theelectrically conducting particles, it has been further found that whenthe relationship of 12≦Mv/Mn≦50 is established assuming that the modevalue in the number distribution in relation to particle size of theelectrically conducting particles is Mn and the mode value in the volumedistribution in relation to particle size of the electrically conductingparticles is Mv, particularly the electric conductivity (weldability,earth property), formability and corrosion resistance can be obtained ina high level. The numerals above are specifying the particle sizedistribution and particularly when many large particles are present inthe particle size as the mode value for the number distribution everyeach particle size, the value becomes large. This is an index differentfrom the maximum particle size and even when the maximum particle sizeis same, the mode value for the volume distribution sometimes differs.If Mv/Mn is less than 12, not only is this unprofitable, by requiring anoperation of removing particles having a large particle size foradjusting the size distribution to such a range, but also theweldability decreases, whereas if Mv/Mn exceeds 50, the formability orcorrosion resistance decreases.

Furthermore, assuming that the thickness of the coat layer is H, therelationship of the mode values with this thickness is specified tosatisfy H/10≦Mv≦10H and 5Mn≦H≦200Mn. Japanese Unexamined PatentPublication (Kokai) No. 01-60668 states that when the index of particlesize and the index of film thickness have a relationship proposedtherein, good performances can be obtained, but the present inventiondiffers from the conventional technique in that the indices used are themode value for the number distribution and the mode value for the volumedistribution as described later and a proper region of the particle sizebased on the film thickness is revealed to be present also in thesmaller region than that heretofore proposed (see, for example, JapaneseUnexamined Patent Publication (Kokai) No. 01-60668). If Mv is less thanH/10, the weldability decreases, whereas if it exceeds 10H, theformability and corrosion resistance decrease. Also, if H is less than5Mn, the corrosion resistance and formability decrease, whereas if itexceeds 200Mn, the weldability decreases.

Within the range specified in the present invention, the formability isalso enhanced than ever before. The reason therefor is because, due toabsence of excessively large particles, the particles exfoliate less atthe shaping and also the cracking of the coating film at the shaping,which takes place in many cases in the vicinity of the interface betweenthe particle and the binder component, is reduced. In addition, thecoating film surface is free from excessive unevenness, so that thecoating film surface can have good slidability and the appearance andcorrosion resistance after a draw-bead test or the like can also getbetter. The same applies to the draw-forming.

By virtue of good formability and no exfoliation or damage to a part ofthe coating film, the corrosion resistance is also enhanced.Particularly, in the case of using a particle having a rust-preventiveeffect, such as ferrosilicon, the increase in the surface area of theparticle also provides an effect of enhancing the corrosion resistance.

When Mn of 0.05 to 1.5 μm and Mv of 2 to 30 μm are satisfied, the effectis particularly high and the weldability, formability and corrosionresistance become good. At the same time, when the film thickness isfrom 2 to 20 μm, a more remarkable effect is obtained. In addition tothese, when the condition that the maximum particle size is 35 μm orless is satisfied, a remarkable effect can be also obtained.

The electrically conducting particles for use in the present inventionmay be a known substance. For example, when a particle comprising (i) ametal and/or (ii) an alloy or compound of a typical metal, transitionmetal or semimetal element is added, functions of, for example,enhancing the electric resistance weldability or corrosion resistancecan be imparted to the coated steel sheet.

For the electrically conducting particles, such a material may be usedafter shaping it into a particle by a known method, for example, bygrinding a solid or jetting out a melt into a gas or aqueous phase.

Examples of the particle which can be used include metals such asmagnesium, aluminum, silicon, calcium, scandium, titanium, vanadium,chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium,germanium, strontium, yttrium, zirconium, niobium, molybdenum,technetium, ruthenium, rhodium, palladium, silver, gold, cadmium, indiumand tin, and alloys and compounds of magnesium, aluminum, silicon,phosphorus, calcium, scandium, titanium, vanadium, chromium, manganese,iron, cobalt, nickel, copper, zinc, gallium, arsenic, strontium,yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium,palladium, silver, cadmium, indium, tin, antimony or tellurium.

Among these electrically conducting particles, those which can be stablyavailable in industry at a relatively low cost include magnesium,aluminum, silicon, chromium, iron, nickel, zinc, tin, copper,zinc-aluminum alloy, zinc-aluminum-magnesium alloy,zinc-aluminum-magnesium-silicon alloy, zinc-iron alloy, zinc-chromiumalloy, zinc-nickel alloy, iron-nickel alloy, iron-chromium alloy,stainless steel, iron-based compounds such as ferrosilicon,ferrophosphorus and ferromanganese, oxide-based particles such as NiOand ZnO, and carbon-based particles such as carbon black, graphite andcarbon nanotube. The form of the particle is not particularly limitedand examples thereof include lump, flake, spherical, amorphous, fiber,whisker and chain.

In order to realize higher corrosion resistance of the coated steelsheet, silicon is preferably used as the essential component in theelectrically conducting particle. Ferrosilicon is electricallyconducting and itself has an effect of enhancing the corrosionresistance. The mechanism of enhancing the corrosion resistance is notfully elucidated, but it is presumed to be that, when an alkalienvironment is created below the coating film due to corrosion,ferrosilicon dissolves and forms a strong silica film, therebypreventing corrosion. Therefore, even if another rust-preventive pigmentfor enhancing the corrosion resistance is not incorporated, sufficientlyhigh corrosion resistance is exhibited and the cause of inhibiting theelectric conductivity can be decreased. The silicon content in theparticle is preferably 20 mass % or more, more preferably 50 mass % ormore.

When the particle size distribution and the content are in respectiveranges specified in the present invention or when the particle size andthe film thickness are in respective ranges specified in the presentinvention, very good formability is attained. The ferrosilicon includesthose differing in the silicon content, but in the present invention,ferrosilicon having a silicon content of 70 mass % or more isparticularly preferred. More specifically, when JIS No. 2 ferrosiliconhaving an silicon content of 75 to 80 mass % or the like is used as theelectrically conducting particle, the electric conductivity can beensured and at the same time, the corrosion resistance is remarkablyenhanced.

Of course, for enhancing the weldability or electric conductivity, aplurality of electrically conducting particles may be used. When theelectrically conducting particles newly added has a particle sizedistribution in the above-described range specified in the presentinvention, the electrically conducting particles have no particularproblem and can be used by appropriately mixing it such that the totalcontent of electrically conducting particles in the coat layer is from15 to 60 vol %. However, when the electrically conducting particlesnewly added have a particle size distribution out of the above-describedrange, the content thereof is preferably 5 vol % or less in the coatlayer. If its content exceeds 5 vol %, the particle size distribution isincreased in the non-uniformity and reduction of the formability isreadily incurred.

In the present invention, the electrically conducting particle containedin the coat layer is in that state that the entire or a part thereof isburied. The coat layer contains, in addition to the electricallyconducting particle, a binder component for holding the coat layer andfor the binder component, conventionally known techniques can be used.For example, in the case where the binder component is an organic resin,examples of the resin include urethane resin, epoxy resin, acryl resin,polyester resin, fluororesin, silicon resin, polyolefin resin, butyralresin, ether resin, sulfone resin, polyamide resin, polyimide resin,amino resin, phenol resin, vinyl chloride resin, polyvinyl alcoholresin, isocyanate resin, and a copolymer resin, a mixture and acomposite material thereof. An inorganic film or organic-inorganiccomposite film formed by a sol-gel method or the like may also be used.The resin may be selected from known techniques such as a resin which iscured and dried at an ordinary temperature, a resin which is cured anddried under heat, and a resin which is cured and dried with energy suchas ultraviolet light or electron beam. Also, the coated metal sheet maybe produced by laminating a film mainly comprising such a resin.

In addition to this resin, the coat layer may contain additives such aswax for imparting lubricity, defoaming agent, leveling agent anddispersant.

Among those resins, particularly when a urethane bond-containing resinis used in the coat layer, the corrosion resistance, formability andelectric conductivity in particular can be attained at the same time ina high level. The reason therefor is considered, for example, becausethe urethane bond-containing resin has excellent flexibility and when apressure is applied by an electrode for welding, is deformed to ensureparticularly the contact of electrically conducting pigments with eachother, the coating film is likely prevented from cleavage or cracking atthe forming by virtue of the flexibility and since this is a chemicallystrong bond, the coating film is highly resistant against degradation.

In regard to the corrosion resistance of the formed part, the film isrequired to have high formability because the film is formed togetherwith the steel sheet, and to satisfy this requirement, a urethanebond-containing resin film using a combination of a polyester polyolhaving at least three functional groups with a blocked organicpolyisocyanate or a blocked product of an organic polyisocyanate and anactive hydrogen compound is preferably formed, whereby an excellent filmhaving good followability to the bend or draw deformation in the pressforming, high hardness and high resistance against chemicals can beobtained. Also, when the urethane bond-containing resin is compoundedwith an epoxy resin having at least one secondary hydroxyl group or withan adduct of a lactone compound or alkylene oxide to an epoxy resin,more excellent properties can be obtained.

The polyester polyol (1) having at least three functional groups used inthe resin for use in the present invention can be obtained byesterifying a dicarboxylic acid, a glycol and a polyol having at leastthree OH groups.

Examples of the dicarboxylic acid for use in the production of thepolyester polyol include aliphatic dicarboxylic acids such as succinicacid, succinic anhydride, adipic acid, azelaic acid, sebacic acid,dodecane diacid, maleic acid, maleic anhydride, fumaric acid, itaconicacid and dimeric acid, and aromatic and alicyclic dicarboxylic acidssuch as phthalic acid, phthalic anhydride, isophthalic acid, dimethylisophthalate, terephthalic acid, dimethyl terephthalate,2,6-naphthalenedicarboxylic acid, hexahydrophthalic anhydride,tetrahydrophthalic anhydride, cyclohexanedicarboxylic acid, dimethylcyclohexanedicarboxylate, methyl hexahydrophthalic anhydride, himicanhydride and methyl himic anhydride.

Examples of the glycol include aliphatic glycols such as ethyleneglycol, diethylene glycol, propylene glycol, 1,3-butylene glycol,1,4-butylene glycol, dipropylene glycol, 1,5-pentanediol,1,6-hexanediol, neopentyl glycol, neopentyl glycol ester of hydroxydivaric acid, triethylene glycol, 1,9-nonanediol,3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol,2-ethyl-1,3-hexanediol, 2,4-diethyl-1,5-pentanediol, polycaprolactonediol, polypropyrene glycol polytetramethylene ether glycol,polycarbonate diol, 2-n-butyl-2-ethyl-1,3-propanediol and2,2-diethyl-1,3-propanediol, and aliphatic or aromatic glycols such ascyclohexanedimethanol, cyclohexanediol,2-methyl-1,1-cyclohexanedimethanol, xylylene glycol, bis-hydroxyethylterephthalate, 1,4-bis(2-hydroxyethoxy)benzene, hydrogenated bisphenolA, ethylene oxide adduct of bisphenol A, and propylene oxide adduct ofbisphenol A.

Examples of the polyol having at least three OH groups include glycerin,trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol,pentaerythritol, diglycerin, and an ethylene oxide adduct, a propioneoxide adduct and ε-caprolactone adduct using such a polyol as aninitiator.

The esterification reaction is performed by charging the polyolcomponent in excess of the acid component and distilling out thecondensate in a usual manner, but since the product is polyfunctional,if the reaction excessively proceeds, gelling may occur. Therefore, thereaction is preferably stopped at an acid value of usually from 0.1 to50, more preferably from 1 to 20. As for the specific production method,for example, a dicarboxylic acid is charged in excess of the molarnumber of glycol, the condensed water is removed while blowing anitrogen gas at a temperature of 180 to 260° C., the reaction is allowedto proceed until a predetermined acid value to obtain a polyesterifiedproduct having a COOH group at both ends, a polyol having at least threeOH groups is charged to convert the ends of this polyesterified productinto an OH group, the condensed water is removed by distillation in thesame manner, and the reaction is stopped at an acid value of 50 or less,preferably from 1 to 20. In the case of using a dimethyl ester ofdicarboxylic acid, this ester is charged in a molar number larger thanthat of glycol and a transesterification reaction is performed under thesame conditions as above, whereby a polyester polyol is obtained. In thecase of using an acid anhydride in combination, a dicarboxylic acid isfirst charged in a molar number smaller than that of glycol, thecondensate is distilled out under the same conditions as above to obtaina polyesterified product having an OH group at both ends, a dicarboxylicanhydride is then added, a polyesterified product having a COOH group atboth ends is obtained by the ring-opening reaction, a polyol having atleast three OH groups is then charged, and a reaction is performed inthe same manner as above, whereby a polyester polyol is obtained. Thepolyester polyol for use in the present invention preferably has afunctional group number of 3 to 7, more preferably from 4 to 6, a numberaverage molecular weight of 600 to 3,500, and a hydroxyl group value of80 to 460. If the functional group number is less than 3, the hardnessof the cured film becomes low and the resistance to chemicals isworsened, whereas if it exceeds 7, a film having bad bending resistancemay result. If the number average molecular weigh is less than 600, thesmoothness of the cured film becomes bad, whereas if it exceeds 3,500, aproblem may arise in the coating operation or the fouling resistance maydecrease. Also, if the hydroxyl group value exceeds 460, the film may beworsened in the bending resistance

The blocked product as the component (b) used in the resin for use inthe present invention is a compound having at least two NCO groups andexamples thereof include aliphatic diisocyanates such as trimethylenediisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate,pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylenediisocyanate, 1,3-butylene diisocyanate, 2,4,4- or2,2,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanateand 2,6-diisocyanate methylcaproate, cycloalkylene-based diisocyanatessuch as 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate,1,3-cyclohexane diisocyanate, 3-isocyanatemethyl-3,5,5-trimethylhexylisocyanate, 4,4′-methylenebis(cyclohexylisocyanate),methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexanediisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane,1,4-bis(isocyanatomethyl)cyclohexane,1,3-bis(isocyanatomethyl)cyclohexane andtrans-cyclohexane-1,4-diisocyanate, aromatic diisocyanates such asm-xylene diisocyanate, m-phenylene diisocyanate, p-phenylenediisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene diisocyanate,4,4′-diphenylmethane diisocyanate, 2,4- or 2,6-tolylene diisocyanate,4,4′-toluidine diisocyanate, dianisidine diisocyanate and4,4′-diphenylether diisocyanate, aromatic aliphatic diisocyanates suchas ω,ω′-diisocyanato-1,3-dimethylbenzene,ω,ω′-diisocyanato-1,4-dimethylbenzene,ω,ω′-diisocyanato-1,4-diethylbenzene andα,α,α′,α′-tetramethylmeta-xylylene diisocyanate, triisocyanates such astriphenylmethane-4,4,4″-triisocyanate, 1,3,5-triisocyanatobenzene,2,4,6-triisocyanatotoluene andω-isocyantoethyl-2,6-diisocyanatocaproate, blocked tetraisocyanates suchas 4,4′-diphenylmethylmethane-2,2′,5,5′-tetraisocyanate, blockedproducts of a derivative from an isocyanate compound, such as dimer,trimer, buiret, allophanate, carbodiimide, polymethylenepolyphenylpolyisocyanate (crude MDI, c-MDI or polymeric MDI) and crude TDI, andblocked products of a prepolymer having an NCO group at the end obtainedby the reaction of such a compound with an active hydrogen compound.

In the case where the organic film is required to have weatherresistance, among those compounds having an NCO group, preferred areisocyanates compounds such as hexamethylene diisocyanate,3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate,1,4-bis(isocyanatomethyl)cyclohexane,1,3-bis(isocyanatomethyl)cyclohexane,4,4′-methylenebis(cyclohexylisocyanate),α,α,α′,α′-tetramethylmeta-xylylene diisocyanate.

The prepolymer having an NCO group at the end obtained by the reactionof such an isocyanate compound with an active hydrogen compound can beobtained by reacting an isocyanate monomer described above with anactive hydrogen compound in the state of excess isocyanate group.Examples of the active hydrogen compound used for the production of thisprepolymer include low molecular weight polyols such as dihydric alcohol(e.g., ethylene glycol, propylene glycol, 1,2-butylene glycol,1,3-butylene glycol, 1,6-hexanediol, diethylene glycol, dipropyleneglycol, neopentyl glycol, neopentyl glycol ester of hydroxy divaricacid, triethylene glycol, hydrogenated bisphenol A, xylylene glycol,1,4-butylene glycol), trihydric alcohol (e.g., glycerin,trimethylolethane, trimethylolpropane, 1,2,6-hexanetriol) andtetrahydric alcohol (e.g., pentaerythritol), and high molecular weightpolyols such as polyether polyol (e.g., propylene oxide or ethyleneoxide adduct of a polyol described above), polyester polyol obtained byreacting a low molecular weight polyol described above with adicarboxylic acid, and polyester polyol aliphatic-modified at itsproduction. These polyols may be used individually or in combination.

The prepolymer can be obtained by performing a reaction usually at 40 to140° C., preferably from 70 to 100° C. with an NCO group/OH groupequivalent ratio of generally about 2.0 to 15, preferably about 4.0 to8.0, and then, if desired, removing the unreacted isocyanate monomer bya commonly employed thin-film distillation method or extraction method.In this reaction, an organic metal catalyst such as tin-based,lead-based, zinc-based or iron-based catalyst may be used.

The blocked product of the above-described isocyanate monomer or aprepolymer thereof can be obtained by reacting the isocyanate monomer ora prepolymer thereof with a blocking agent by a known method. Theblocking agent for use in this reaction may be any type blocking agentsuch as phenol-based, lactam-based, active methylene-based, activemethylene-based, alcohol-based, mercaptan-based, acid amide-based,imide-based, amine-based, imidazole-based, urea-based, carbamate-based,imine-based, oxime-based or sulfite-based blocking agent. In particular,a blocking agent such as phenol-based, oxime-based, lactam-based orimine-based blocking agent is advantageously used. Specific examples ofthe blocking agent include the followings.

Phenol-Based Blocking Agent:

Phenol, cresol, xylenol, nitrophenol, chlorophenol, ethylphenol,p-hydroxydiphenyl, tert-butyl ether, o-isopropylphenol,o-sec-buylphenol, p-nonylphenol, p-tert-octylphenol, hydroxybenzoicacid, hydroxybenzoic acid ester, etc.

Lactam-Based Blocking Agent:

ε-Caprolactam, δ-valerolactam, γ-butyrolactam, β-propiolactam, etc.

Active Methylene-Based Blocking Agent:

Diethyl malonate, dimethyl malonate, ethyl acetoacetate, methylacetoacetate, acetylacetone, etc.

Alcohol-Based Blocking Agent:

Methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,isobutyl alcohol, tert-butyl alcohol, n-amyl alcohol, tert-amyl alcohol,lauryl alcohol, ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, ethylene glycol monobutyl ether, diethylene glycolmonomethyl ether, distyrene glycol monoethyl ether, propylene glycolmonomethyl ether, benzyl alcohol, methoxymethanol, glycolic acid,glycolic acid esters such as methyl glycolate, ethyl glycolate and butylglycolate, lactic acid, lactic acid esters such as methyl lactate, ethyllactate and butyl lactate, methylolurea, methylolmelamine, diacetonealcohol, ethylene chlorohydrin, ethylene bromohydrin,1,3-dichloro-2-propanol, ω-hydroperfluoroalcohol, acetocyanhydrine, etc.

Mercaptan-Based Blocking Agent:

Butylmercaptan, hexylmercaptan, tert-butylmercaptan,tert-dodecylmercaptan, 2-mercaptobenzothiazol, thiophenol,methylthiophenol, ethylthiophenol, etc.

Acid Amide-Based Blocking Agent:

Acetanilide, acetanisidide, acetotoluide, acrylamide, methacrylamide,acetic amide, stearic amide, benzamide, etc.

Imide-Based Blocking Agent:

Succinic imide, phthalic imide, maleic imide, etc.

Amine-Based Blocking Agent:

Diphenylamine, phenylnaphthylamine, xylidine, n-phenylxylidine,carbazole, aniline, naphthylamine, butylamine, dibutylamine,butylphenylamine, etc.

Imidazole-Based Blocking Agent:

Imidazole, 2-imidazole, etc.

Urea-Based Blocking Agent:

Urea, thiourea, ethyleneurea, ethylenethiourea, 1,3-diphenylurea, etc.

Carbamate-Based Blocking Agent:

Phenyl n-phenylcarbamate, 2-oxazolidone, etc.

Imine-Based Blocking Agent:

Ethyleneimine, propyleneimine, etc.

Oxime-Based Blocking Agent:

Formamidoxime, acetoaldoxime, acetoxime, methyl ethyl ketoxime, diacetylmonoxime, benzophenone oxime, cyclohexane oxime, etc.

Sulfite-Based Blocking Agent:

Sodium bisulfite, potassium bisulfite, etc.

Specific methods for reacting the isocyanate monomer or a prepolymerthereof with a blocking agent include a method of reacting theisocyanate monomer or a prepolymer thereof with a blocking agent bysetting the equivalent ratio of NCO group/active hydrogen group inblocking agent to about 0.9 to 1.0, preferably about 0.95 to 1.00, amethod of reacting the isocyanate monomer with a blocking agent bysetting the equivalent ratio of NCO group/active hydrogen group inblocking agent to about 1.1 to 3.0, preferably about 1.2 to 2.0, andthen reacting it with the above-described low molecular weight polyol,high molecular weight polyol, water or lower amine for use in theproduction of the prepolymer, and a method of reacting the isocyanatemonomer with the low molecular weight polyol, high molecular weightpolyol, water or lower amine at an NCO group/active hydrogen groupequivalent ratio of about 1.6 to 10.0, preferably from about 2.0 to 7.0,and then reacting it with a blocking agent. Each reaction above isperformed by a known method in a solvent not having an active hydrogengroup (examples of this solvent include aromatic solvents such asbenzene, toluene and xylene, petroleum-based solvents such asSolvesso-100 and Solvesso-200, ester-based solvents such as ethylacetate and butyl acetate, ketone-based solvents such as acetone, methylethyl ketone, methyl isobutyl ketone and cyclohexanone, and ether-basedsolvents such as tetrahydrofuran) or in the absence of such a solvent.At the reaction, a known catalyst such as tertiary amine and organicmetal may be used.

In the present invention, when (c) an epoxy resin having at least onesecondary hydroxyl group or an adduct thereof is further added to thepolyol component, more excellent properties can be obtained. Examples ofthe lactone compound or alkylene oxide adduct of an epoxy resin havingat least one secondary hydroxyl group include those obtained by adding alactone compound or an alkylene oxide to an epoxy resin represented bythe following formula according to a known method.

(wherein X represents a phenylene or cyclohexylene group which may besubstituted by a halogen, and n represents a number of 0.5 to 12.0).

The amount of the lactone compound or alkylene oxide added isapproximately from about 5 to 40 parts by weight per about 95 to 60parts by weight of the epoxy resin. More preferably, the amount of thelactone compound or alkylene oxide added is from about 10 to 30 parts byweight per about 90 to 70 parts by weight of the epoxy resin.

Among the epoxy resins represented by the formula above, those where Xis a p-phenylene group and n is a number of 2 to 9 are preferred.Examples of the halogen include bromine and chlorine. The number ofsubstituents is usually on the order of 1 to 3, and the positiontherefor may be any position of the phenylene or cyclohexylene group.

Examples of the lactone compound include β-propionlactone,butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone,δ-caprolactone and ε-caprolactone, with ε-caprolactone being preferred.Examples of the alkylene oxide include ethylene oxide, propylene oxide,styrene oxide, glycidyl methacrylate and epichlorohydrin, with ethyleneoxide being preferred.

In the polyol component, the blending ratio of the epoxy resin having atleast one secondary hydroxyl group or the adduct obtained by adding alactone compound or an alkylene oxide to the epoxy resin is from about10 to 70 mass %, preferably from about 10 to 60 mass %. If the blendingratio is less than 10 mass %, the resistance against chemicals may beworsened, whereas if it exceeds 70 mass %, the hardness is seriouslydecreased and damages are readily generated at the press forming.

The raw material film-forming resin for use in the present inventioncontains the polyols (a) and (c) and the blocked product (b) and as forthe blending ratio between the polyols and the blocked product, the OHgroup (a hydroxide group)/regenerated NCO group equivalent ratio ispreferably from about 1/2 to 2/1, more preferably 1/1.2 to 1/0.8.

In the case where the coat layer mainly comprises a thermoplastic resin,a coated metal sheet excellent particularly in the weldability isobtained. This is presumed to result because the thermoplasticity isexerted upon application of a pressure by the electrode for welding andthe coat layer is compressed, as a result, a firmer contact betweenelectrically conducting particles is ensured and the welding currentstably flows. Furthermore, by virtue of flexibility of the thermoplasticresin, cracking or separation of the coat layer can be reduced and thecorrosion resistance is enhanced. Examples of the thermoplastic resininclude polyethylene terephthalate resin (PET), high-molecular polyesterresin, low-density polyethylene resin, high-density polyethylene resin,chained low-density polyethylene resin, polypropylene resin, polystyreneresin, acrylonitrile butadiene styrene resin (ABS resin), polyacetalresin (POM), polycarbonate resin, polyphenylene sulfide resin, polyamideresin and fluororesin.

In order to enhance the corrosion resistance, one or morerust-preventive pigment and/or silica may be added. The content thereofin the coat layer is preferably 20 vol % or less, more preferably 15 vol% or less. If the content exceeds 20 vol %, the electric conductivityand formability, in particular, are liable to decrease.

Examples of the rust-preventive pigment include hexavalent chromatessuch as strontium chromate and calcium chromate. In the case ofintending to avoid use of a hexavalent chromium compound as therust-preventive pigment, for example, a compound capable of releasingone or more ion out of silicate ion, phosphate ion and vanadate ion,such as calcium silicate, aluminum silicate, magnesium phosphate,aluminum phosphate, phosphorus vanadate and aluminum vanadate, may beused. When fine particulate silica is further added thereto, the scratchresistance, film adhesion and corrosion resistance are enhanced.Examples of the fine particulate silica include fumed silica, colloidalsilica and aggregated silica. A calcium-deposited silica may also beused.

The rust-preventive pigment which can be preferably used is, forexample, a known rust-preventive pigment such as hexavalent chromate(e.g., strontium chromate, calcium chromate).

In the case of intending to avoid use of a hexavalent chromium compoundas the rust-preventive pigment, for example, a compound capable ofreleasing one or more ion out of silicate ion, phosphate ion andvanadate ion may be used.

For example, a rust-preventive pigment capable of releasing vanadate ionand phosphate ion is described below. When the rust-preventive pigmentreleases these two ions, the oxidizer function unsatisfied only byphosphate ion can be supplemented by the vanadate ion. In other words,this rust-preventive pigment serves, in an environment where water andoxygen are present, as a phosphate ion source of releasing phosphate ionand as a vanadate ion source of releasing vanadate ion.

In order to bring out the rust-preventive power of the organic film,this can be attained when phosphate ion and vanadate ion are presenttogether in the organic film. The phosphate ion and vanadate ion may beas-is present or a substance capable of releasing phosphate ion andvanadate ion in an environment allowing for the presence of water andoxygen may be contained. The phosphate ion is scarcely present by itselfin an aqueous solution and is present in various forms such ascondensate, but also in such a case, the concept of “phosphate ion” asused in the present invention should be understood to include thecondensate vanadate ion. The phosphate ion source and vanadate ionsource are mainly provided as a rust-preventive pigment and this pigmentcan be obtained by baking and grinding a mixture containing a phosphoruscompound, a vanadium compound and if desired, one or both of anetwork-modifying ion source and a vitrified substance.

Examples of the phosphide used in the rust-preventive pigment includeorthophosphoric acid, condensed phosphorus, orthophosphate or condensedphosphate of various metals, phosphorus pentoxide, phosphate minerals,commercially available composite phosphate pigments, and a mixturethereof. The orthophosphate as used herein includes a monohydrogen salt(HPO₄ ²⁻) and a dihydrogen salt (H₂PO₄ ⁻) thereof. Also, the condensedphosphate includes hydrogen salts thereof. Furthermore, the condensedphosphate includes metaphosphates, normal polyphosphates and normalpolymetaphosphates. Specific examples of the phosphorus compound includephosphate minerals such as monetite, triphylite, whitlockite, xenotime,stercorite, struvite and vivianite, commercially available compositephosphate pigments such as silica polyphosphate, composite phosphoricacids such as pyrophosphoric acid and metaphosphoric acid, compositephosphates such as metaphosphate, tetrametaphosphate, hexametaphosphate,pyrophosphate, acidic pyrophosphate and tripolyphosphate, and a mixturethereof. The metal species for forming the phosphate is not particularlylimited and examples thereof include alkali metals, alkaline earthmetals, other metal species of typical element, and transition metals.Preferred examples of the metal species include magnesium, calcium,strontium, barium, titanium, zirconium, manganese, iron, cobalt, nickel,zinc, aluminum, lead and tin.

Other than these, oxo-cations such as vanadyl, titanyl and zirconyl canalso be used. Among these, more preferred are calcium and magnesium. Thealkali metal is preferably not used in a large amount. When a phosphateof an alkali metal is used, the baked product tends to be excessivelydissolved in water. However, in the case of using a phosphate of analkali metal, the solubility in water may be controlled, if possible, atthe production of the rust inhibitor or at other stages. This controlmay be performed by various methods such as use or coating of a matrixmaterial (particularly, vitrified substance) for preventing dissolutionin water.

The vanadium compound used in the rust-preventive pigment is a compoundhaving a vanadium valence of 0, 2, 3, 4 or 5 or having two or more ofthese vanadium valences, and examples thereof include their oxides,hydroxides, oxyacid salts with various metals, vanadyl compounds,halides, sulfates and metal powder. This compound dissolves underheating or in the presence of water and acts with oxygen into a compoundof higher valence. For example, the metal powder or divalent compound isfinally converted into a trivalent, tetravalent or pentavalent compound.A rust-preventive pigment containing a pentavalent vanadium compound asone component is preferred. The zerovalent compound, such as vanadiummetal powder, may be used because of the above-described reason, butthis compound has a problem, for example, the oxidation reaction isinsufficient, and its use is not preferred in practice. The pentavalentvanadium compound has vanadate ion and readily reacts with phosphate ionunder heating to form a heteropolymer. Specific examples of the vanadiumcompound include vanadium(II) compounds such as vanadium(II) oxide andvanadium(II) hydroxide, vanadium(III) compounds such as vanadium oxide,vanadium(IV) compounds such as vanadium(IV) oxide and vanadyl halide,vanadium(V) compounds such as vanadium(V) oxide, vanadates such asorthovanadate, metavanadate or pyrovanadate with various metals andvanadyl halide, and a mixture thereof. Examples of the metal species forthe vanadate are the same as those described for the phosphate. Thevanadium compound may also be prepared by baking a vanadium oxide withan oxide, hydroxide, carbonate or the like of various metals at 600° C.or more. Also in this case, the alkali metal is not so preferred in viewof solubility, but when the solubility is controlled by an appropriatetreatment described regarding the phosphate, the alkali metal may beused. The same applies to the halide and sulfate.

The ratio of phosphate ion source to vanadate ion source blended ispreferably from 1:3 to 100:1 in terms of the molar ratio of P₂O₅ toV₂O₅.

The total amount of the electrically conducting particle and therust-preventive pigment blended in the organic coat layer of the presentinvention is from 6 to 65 vol %, preferably from 20 to 60 vol %, per 100parts by weight of the entire solid content in the coating material forthe organic film layer. If this total amount is less than 6 vol %, theabove-described effects by virtue of the addition are not satisfactorilybrought out, whereas if it exceeds 65 vol %, the cohesion of the filmafter curing decreases and a sufficiently high film strength cannot beobtained. Out of these components, the amount of the rust-preventivepigment blended is from 1 to 40 vol %, preferably from 3 to 30 vol %. Ifthe amount blended is too small, a sufficiently high rust-preventivepower cannot be obtained, whereas if it is excessively large, theproportion of the film resin decreases for that portion to causereduction in the cohesion of film or the proportion of the electricallyconducting particle decreases to fail in ensuring satisfactoryweldability on the occasion of required electric welding.

The metal material may be a known metal material and examples thereofinclude steel sheet, copper sheet, titanium sheet and aluminum sheet.Examples of the steel sheet include various plated steel sheets,stainless steel sheet, cold-rolled steel sheet and hot-rolled steelsheet. Examples of the plated steel sheet include zinc-plated steelsheet, zinc alloy-plated steel sheet, alloyed zinc-plated steel sheet,tin-plated steel sheet, tin alloy-plated steel sheet, chromium-platedsteel sheet, chromium alloy-plated steel sheet, aluminum-plated steelsheet, aluminum alloy-plated steel sheet, nickel-plated steel sheet,nickel alloy-plated steel sheet, copper-plated steel sheet, copperalloy-plated steel sheet, iron-plated steel sheet, iron alloy-platedsteel sheet, iron-phosphor composite-plated steel sheet,manganese-plated steel sheet, lead-plated steel sheet, andcomposite-plated steel sheet with the plating being constituted by ametal or alloy containing fine particles such as silica.

In particular, when a zinc or zinc-based alloy-plated steel sheet (forexample, electrogalvanized steel sheet, hot-dip galvanized steel sheet,alloyed hot-dip galvanized steel sheet, zinc-nickel alloy-plated steelsheet, zinc-aluminum alloy-plated steel sheet or zinc-aluminum-magnesiumalloy-plated steel sheet) is used, the product metal material can besuitably used as a primer steel sheet for automobiles, which isexcellent in the profitability and corrosion resistance, or as a coatedsteel sheet for home appliances and OA devices, where earth property isrequired. Also, when an aluminum or aluminum-based alloy-plated steelsheet (for example, aluminum-silicon plated steel sheet oraluminum-zinc-silicon alloy-plated steel sheet) is used, the productmetal material can be suitably used as a highly anticorrosive coatedsteel sheet for building materials, and when a tin-based alloy-platedsteel sheet (for example, tin-zinc alloy-plated steel sheet) or a zincalloy-plated steel sheet (for example, zinc-nickel alloy-plated steelsheet) is used, the product metal material can be suitably used as acoated steel sheet for fuel tanks. In addition, when an aluminum sheethaving poor weldability is used as the base sheet, the product metalmaterial can be suitably used as a primer steel sheet for automobiles,which is excellent in weldability.

With respect to the underlying steel sheet for use in the presentinvention, various steel sheets can be used, such as aluminum-killedsteel sheet, very low carbon steel sheet having added thereto titanium,niobium or the like, and high-strength steel obtained by adding astrengthening element such as phosphorus, silicon or manganese to such asteel sheet. This steel sheet may be plated with various metals oralloys described above. The plating coverage is not particularly limitedbut is preferably 10 g/m² or more in view of corrosion resistance and100 g/m² or less in view of weldability.

Furthermore, in the present invention, the surface roughness of theorganic coat layer is controlled to from 0.3 to 2.5 μm as Ra, preferably20 μm or less as Rmax, and the Pc of the surface texture is controlledto from 10 to 200 peaks per 10-mm length with a count level of 0.3 μm,whereby the formability and continuous workability of welding canenhanced. These conditions for the surface roughness and surface textureand a production method using the conditions have been found as a resultof studies on good formability and corrosion resistance obtainable basedon the embodiment of the organic resin and good weldability andcorrosion resistance obtainable based on the embodiment of theelectrically conducting particle so as to effectively bring out theseproperties at the same time.

The surface roughness and texture can be controlled by adjusting thecoating material and, for example, adjusting the viscosity of thecoating material, adding a leveling agent, adding a surfactant, adding asolvent having a different specific gravity, or adding a filler having acontrolled particle size. The surface can also be adjusted by amechanical method such as temper-rolling with a skin pass roll orsurface control by shot blasting. If the center line average roughnessRa is less than 0.3 μm, the contact area with the metal mold at theforming increases to elevate the coefficient of friction and this causesreduction in the formability, whereas if it exceeds 2.5 μm, thecontinuous workability at the welding decreases. Accordingly, Ra is from0.3 to 2.5 μm, preferably from 0.6 to 1.5 μm. Also, if the maximumheight Ra exceeds 20 μm, an irregular portion is locally generated inthe regular roughness specified by Ra and uneven electrification such aslocal electrification is readily caused in this portion and, as aresult, continuous formability at the welding decreases. Accordingly,Rmax is 20 μm or less. The peak count Pc is from 10 to 200 peaks per10-mm length with a count level of 0.3 μm. If the Pc is less than 10peaks, the contact area with the metal mold at the forming increases toelevated the coefficient of friction and this causes reduction in theformability, whereas if Pc exceeds 200 peaks, the texture largelyfluctuates at every place and continuous workability at weldingdecreases. Particularly, when these three parameters are simultaneouslysatisfied, the weldability, formability and corrosion resistance aremore enhanced. The surface roughness and texture can be measured by anormal roughness meter. The roughness per 10-mm length at an arbitraryportion is measured for L direction and C direction of the steel sheetand the aptitude is judged by whether each value falls within the rangespecified in the present invention. Alternatively, the aptitude may bejudged by measuring the surface roughness and texture by athree-dimensional roughness meter and converting the obtained valuesinto two-dimensional expression.

Furthermore, particularly in the case of use for a fuel tank, the metalmaterial is preferably a tin-based alloy-plated steel sheet, though themetal material is not limited thereto. tin has very good corrosionresistance against an organic acid generated due to oxidativedegradation of gasoline and also, the tin plating exhibits excellentspreadability even in the severe press forming and therefore, properlyfollows the deformation of steel sheet. By combining such propertieswith the protective activity of the electrically conductingpigment-containing organic film coat, very good corrosion resistance andformability are exerted and at the same time, good weldability can beensured. When a system where an element having a sacrificinganticorrosive activity is alloyed with the tin plating is used, moreexcellent corrosion resistance can be obtained. The tin plating ortin-based alloy plating is advantageous also in view of cost, becausethe inner surface can have good corrosion resistance against degradedgasoline and the coating can be omitted.

The tin plating or tin-based alloy plating is a tin plating or an alloyplating comprising tin and one or more metal of zinc, aluminum,magnesium and silicon and having a composition that tin accounts for 50mass % or more of the entire. Particularly, the zinc-alloyed tin platingcan additionally have the sacrificing anticorrosive activity of zinc andis preferred as compared with the tin plating. At this time, the amountof zinc added is preferably 1 mass % or more for exerting thesacrificing anticorrosive activity. Also, when aluminum and magnesiumare added to tin or tin-zinc plating, this is preferred in view ofcorrosion resistance. Magnesium exerts by itself an effect of enhancingthe corrosion resistance but, for example, a compound such as Mg₂tin orMg₂Si is formed in the process of producing a molten plating andpreferentially dissolves in a corrosive environment and this causes amagnesium-based film to cover the plating layer and the base iron,whereby an anticorrosive effect is brought out. The amount of magnesiumadded for providing such an effect is preferably 0.5 mass % or more.Magnesium is an element having a very strong affinity for oxygen and,for example, in the case of producing the plated steel sheet by hot-dipgalvanization, aluminum is preferably added at the same time forpreventing the oxidation. The operability is improved by adding aluminumin an amount of about 1/10 the amount of magnesium. The aluminum is alsoeffective in inhibiting the oxidation of tin or zinc itself and evenwhen magnesium is not added, the plating appearance can be improved byadding aluminum. If desired, elements such as calcium, lithium, mischmetal and antimony may be further added for the purpose of enhancing thecorrosion resistance or preventing the oxidation.

In the case of use as a tank material, high resistance weldability(e.g., spot welding, seam welding) is required. As the copper of theelectrode readily forms a compound with tin, the plating coveragegreatly affects the weldability. The plating coverage of course has alarge effect also on the corrosion resistance. A larger plating coverageis advantageous in view of corrosion resistance but is disadvantageousin view of weldability and therefore, the plating coverage is preferablyfrom 20 to 50 g/m² per one surface.

Also, high formability is required of the fuel tank and, in thiscontext, an IF steel (interstitial free steel) having excellentformability is preferably applied. In order to ensure weldingairtightness, secondary formability and the like after welding, a steelsheet having added thereto from 0.0002 to 0.003 mass % of boron is morepreferred.

As for the plating method, a conventional production method such aselectroplating, hot-dip plating and vapor phase plating can be used. Theplating can be of course directly applied to the steel sheet or apreplating treatment may be applied before the plating. The preplatingis applied so as to enhance the plating property and may use nickel,cobalt, iron, chromium, tin, zinc, copper or a metal containing such ametal. The thickness is not particularly limited but is usually about0.1 μm.

In use for a fuel tank, the film thickness of the organic coat layer ispreferably from 1.0 to 20 μm. If the film thickness is less than 1.0 μm,even when combined with an undercoating film, the coat layer cannotsatisfactorily contribute to the rust-preventive effect, whereas if itexceeds 20 μm, this is economically disadvantageous because the effectis saturated, and also an adverse effect is caused on the weldability Inorder to more stabilize the corrosion resistance, formability andweldability, the film thickness is more preferably from 5 to 15 μm. Thetotal amount of the electrically conducting pigment and therust-preventive pigment blended in the organic film layer is from 5 to70 vol %, preferably from 20 to 60 vol %, per 100 parts by weight of theentire solid content in the coating material for the organic film layer.If this total amount is less than 5 vol %, the above-described effectsby virtue of the addition are not satisfactorily brought out, whereas ifit exceeds 70 vol %, the cohesion of the film after curing decreases anda sufficiently high film strength cannot be obtained. Out of thesepigments, the amount of the electrically conducting pigment blended isfrom 1 to 50 vol %, preferably from 3 to 40 vol %. If this amountblended is too small, a sufficiently high weldability cannot beobtained, whereas if it is excessively large, the followability of thefilm at the forming decreases. On the other hand, the amount of therust-preventive pigment blended is from 1 to 40 vol %, preferably from 3to 30 vol %. If this amount blended is too small, a sufficiently highrust-preventive power cannot be obtained, whereas if it is excessivelylarge, the proportion of the film resin decreases at that portion tocause reduction in the cohesion of film.

FIG. 1 shows an example of a fuel tank, but the fuel tank of the presentinvention is of course not limited thereto. In FIG. 1, a metal sheet 1 ahaving at least on the outer surface thereof a coat layer 1 b containingan electrically conducting particle is formed, and the formed upper tankportion 1 and the lower tank portion 2 (2 a, 2 b) formed in the samemanner are welded to each other at respective flange portions 1 c and 2c to form a fuel tank. The inner side of the fuel tank may be furthersubjected to a surface treatment, if desired.

For the purpose of enhancing the adhesion between the coat layer and themetal sheet or enhancing the corrosion resistance or electricconductivity, an undercoating layer may be formed on the surfaces ofthese metal sheets. The undercoating layer may be formed by a knowntechnique and examples thereof include a phosphate-based treatment, atrivalent chromic acid treatment, a chromate treatment, azirconium-based treatment, a titanium-based treatment, a manganese-basedtreatment, a nickel-based treatment, a cobalt-based treatment, avanadium-based treatment and a treatment with a coupling agent (forexample, a silicon-based or titanium-based coupling agent) or with anorganic material. The undercoating layer need not be a single layer andmay be formed by combining a plurality of treatments, for example, azinc phosphate treatment layer may be formed and then subjected to asealing treatment or a chromate treatment may be applied afterpre-adjustment by an acidic nickel-containing solution.

The metal sheet surface can be treated by a known method before formingthe undercoating layer or in the case of not forming an undercoatinglayer, before forming the coat layer. Examples of the treating methodinclude degreasing with water, hot water or a degreasing solution, andmechanical grinding by etching with an acid or an alkali or by using abrush or the like.

The undercoating layer may be a film formed, for example, by a method ofcoating•drying an aqueous solution mainly comprising a known hexavalentchromic acid and containing, if desired, a fine particulate silica or asilane coupling agent, a method of forming an undercoating layer bycontacting the plating surface with an aqueous solution mainlycomprising a hexavalent chromic acid and containing, if desired, a fineparticulate silica or a silane coupling agent and then washing anddrying the film, a method of coating and drying an aqueous solutionmainly comprising a trivalent chromic acid but not containing ahexavalent chromic acid, and containing, if desired, a fine particulatesilica or a silane coupling agent, a method of depositing a film mainlycomprising a trivalent chromium on the plating surface throughelectrolysis in an aqueous chromic acid solution and then washing anddrying the film, or a method of depositing a phosphate of zinc and/ornickel and/or iron on the plating surface. One of these methods may beused or a plurality of the methods may be used in combination. Also, afilm formed by coating and drying, on the plating surface, an aqueoussolution mainly comprising an aqueous resin and containing at least onemember selected from a fine particulate silica, a silane coupling agent,tannin and a tannic acid may be used. In the case of intending to avoiduse of hexavalent chromium, a film formed from a trivalent chromium, aphosphate of various metals, or an aqueous resin may be used as theundercoating layer.

The aqueous resin for the undercoating layer includes not only awater-soluble resin but also a resin which is originally insoluble inwater but can provide a state of being finely dispersed in water, suchas emulsion or suspension. Examples of such an aqueous resin which canbe used include a polyolefin-based resin, an acrylolefin-based resin, apolyurethane-based resin, a polycarbonate-based resin, an epoxy-basedresin, a polyester-based resin, an alkyd-based resin, a phenol-basedresin and other thermosetting resins. Among these resins, preferred arecrosslinkable resins, and more preferred are an acrylolefin-based resin,a polyurethane-based resin and a mixed resin of these two resins. Theseaqueous resins may be used by mixing or polymerizing two or morethereof.

The silane coupling agent is firmly bonded to both the zinc orzinc-containing alloy plating and the film in the presence of an organicresin, whereby the adhesion of the film and in turn the corrosionresistance are remarkably enhanced. Examples of the silane couplingagent include γ-(2-aminoethyl)aminopropyltrimethoxysilane,γ-(2-aminoethyl)aminopropymethyldimethoxysilane, aminosilane,γ-methacryloxypropyltrimethoxysilane,N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane,γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane,methyltrimethoxysilane, vinyltrimethoxysialne,octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride,γ-chloropropylmethyldimethoxysilane,γ-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane,dimethyldichlorosilane and trimethylchlorosilane.

In the case of using a silane coupling agent for the undercoating layerformed of an aqueous resin, the content thereof is preferably from 0.1to 3,000 parts by weight per 100 parts by weight of the aqueous resin interms of the solid content. If the content is less than 0.1 part byweight, a sufficiently high adhesive property cannot be obtained at theforming due to insufficient amount of the silane coupling agent and poorcorrosion resistance results, whereas if it exceeds 3,000 parts byweight, the effect of enhancing the adhesive property is saturated andthis is unprofitable.

The tannin or tannic acid in the undercoating layer formed of an aqueousresin has a role of adhering to the zinc or zinc-containing alloyplating layer by firmly reacting therewith, and also adhering to theaqueous resin. The aqueous resin adhered by tannin or tannic acid firmlyadheres to the resin coated thereon, as a result, the plating layerseems to firmly adhere to the film even without use of a chromatetreatment which has been conventionally used. Furthermore, in someportions, the tannin or tannic acid itself is considered to participatein the bonding between the plated steel sheet and the film without theintervention of the aqueous resin.

The tannin or tannic acid is firmly bonded to both the zinc orzinc-containing alloy plating and the film in the presence of an aqueousresin, whereby the adhesion of the film and in turn the corrosionresistance are remarkably enhanced. The tannin or tannic acid may be ahydrolyzable tannin, a condensed tannin or a partially decomposedproduct thereof. Examples of the tannin or tannic acid include, but arenot particularly limited to, hamamelitannin, sumac tannin, gallictannin, myrobolan tannin, divi-divi tannin, algarrobilla tannin, valoniatannin and catechin. A commercially available product such as “TannicAcid: AL” (produced by Fuji Chemical Industry Co., Ltd.) may be used.

As for the tannin or tannic acid content, from 0.2 to 50 parts by weightof tannin or tannic acid is preferably contained per 100 parts by weightof the resin. If the tannin or tannic acid content is less than 0.2parts by weight, the effect by its addition is not obtained and theadhesion of film or corrosion resistance of the formed part isinsufficient, whereas if it exceeds 50 parts by weight, there ariseproblems such as occurrence of gelling during the long-term storage ofthe treating solution.

When a fine particulate silica is further added, the scratch resistance,film adhesion and corrosion resistance are enhanced. The fineparticulate silica as used in the present invention genericallyindicates silicas characterized in that when dispersed in water, a waterdispersion state can be stably maintained by virtue of their fineparticle size and precipitation is not observed semipermanently. Thisfine particulate silica is not particularly limited as long as itcontains less impurities such as sodium and is weakly alkaline. Acommercially available silica such as “tinowtex N” (produced by NissanChemical Industries, Ltd.) and “Adelite AT-20N” (produced by Asahi DenkaKogyo K.K.) may be used.

The fine particulate silica content is, in terms of the solid content,preferably from 1 to 2,000 parts by weight, more preferably from 10 to400 parts by weight, per 100 parts by weight of the aqueous resin. Ifthe content is less than 1 part by weight, the effect obtainable by theaddition is low, whereas if it exceeds 2,000 parts by weight, the effectof enhancing the corrosion resistance is saturated and this isunprofitable. Also, when an etching fluoride is added, the film adhesionis enhanced. Examples of the etching fluoride which can be used includezinc fluoride tetrahydrate and zinc hexafluorosilicate hexahydrate. Theetching fluoride content is, in terms of the solid content, preferablyfrom 1 to 1,000 parts by weight per 100 parts by weight of the aqueousresin. If the content is less than 1 part by weight, the effectobtainable by the addition is low, whereas if it exceeds 1,000 parts byweight, the effect of etching is saturated to give no more improvementin the film adhesion and this is unprofitable.

If desired, a surfactant, a rust inhibitor, a foaming agent and the likemay be added. The coverage of the undercoating layer after drying ispreferably from 10 to 1,000 mg/m². If the coverage is less than 10mg/m², the adhesive property is poor and the corrosion resistance of theformed part is insufficient, whereas if it exceeds 1,000 mg/m², this isnot only unprofitable but also causes reduction in the formability andalso in the corrosion resistance.

The coated metal material of the present invention may be produced by aknown method. The coated steel sheet containing electrically conductingparticles can be produced, for example, by mixing electricallyconducting particles with a binder component to prepare a coatingmaterial and applying the obtained coating material. The film formationcan be performed by a known method according to the binder component orcontained components, for example, by applying heat to volatilize thesolvent or the like or cure the film or irradiating an energy ray tocure the film. As for the coating method, a known method may be used andexamples thereof include roll coater, roller coating, brush coating,curtain coater, die coater, slide coater, electrostatic coating, spraycoating, dip coating and air knife coating. The form of the coatingmaterial is also not particularly limited and may be a powder, a solid,a solvent system or a water system. Also, a solid coating material maybe melted under heating and coated while extruding it from a die.

Alternatively, the coated metal sheet may be produced by previouslykneading an electrically conducting particle in the film layer andlaminating the resulting film. An adhesive may be used for thelamination or the film may be heat-melted and laminated directly on ametal sheet.

In the present invention, the coat layer is sufficient if it is formedat least on one surface of a metal, but may be formed on both surfaces.In the case of forming the coat layer is formed on one layer, the othersurface may be subjected to formation of some treating layer or a coatlayer or may have the metal surface left as it is.

The method for coating the undercoating film is also not particularlylimited and a commonly known coating method such as roll coating,curtain flow coating, air spraying, airless spraying, electrostaticcoating and dipping may be used. The drying and baking after the coatingmay be performed by using a known method such as hot-air furnace,induction heating furnace and near infrared furnace, or by combiningthese methods. Depending on the kind of the aqueous resin used, thecuring may be performed with an ultraviolet ray or an electron beam.Alternatively, the film may be naturally dried without using forceddrying, or after previously heating the plated steel sheet, the film maybe formed thereon and naturally dried.

During such drying and curing or after curing, a process of controllingthe surface roughness and texture, such as shot blasting and skin passrolling, may be provided.

Furthermore, in usage as a fuel tank material, the steel sheet of thepresent invention is used in practice after passing through forming andresistance welding such as seam welding and spot welding in the normalproduction process and therefore, when repair coating is applied afterwelding, high reliability can be obtained. The repair coating materialused here may be a commercially available product and this may besufficient if it can exhibit good adhesion to the organic film andinhibit the penetration of corrosive factors such as moisture. Even whensuch repair coating is performed, the steel sheet of the presentinvention can be produced at a sufficiently low cost as compared withconventional techniques where after-coating is applied. Also in otheruses, some repair coating can be of course applied to the joined part,end face part, form flaw part, handling flaw part or the like for thepurpose of obtaining higher reliability.

EXAMPLES

The present invention is described below by referring to Examples, butthe present invention is not limited to these Examples.

Example 1

Various electrically conducting particles were prepared and ground by agrinder according to the conditions to produce particles having varioussize distributions. A predetermined amount of the electricallyconducting particle was mixed with a urethane-epoxy-based resin and theresulting mixture was coated on a metal sheet, baked and then dried. Insome samples, the organic film was coated after an undercoating film isapplied on the metal sheet. The conditions thereof are shown in Table 1.At this time, the drying condition was 210° C. as a peak metaltemperature. The thus-obtained coated metal sheets were subjected toevaluations of weldability, formability and corrosion resistance underthe following conditions.

(1) Evaluation of Spot Weldability

Spot welding was performed by using a R40 chromium-copper electrodehaving a tip diameter of 5 mm at a welding current of 8 kA under anapplied pressure of 1.96 kN for a welding time of 12 cycles, and thecontinuous dotting number was evaluated by the dotting numberimmediately before the nugget diameter decreased below 3{squareroot}{square root over (t)} (where t=sheet thickness)

(2) Earthing Property

The interlayer resistivity of the coat layer was measured by a Rollesterfour-probe method.

(3) Formability

(a) Cylindrical Deep-Drawing Test

A forming test was performed at a drawing ratio of 2.0 by using acylindrical pounch having a diameter of 50 mm in a hydraulic formingtester. After coating with a rust-preventive oil, the metal sheet wasleft standing for 1 hour to 1 hour and 30 minutes and then tested. Atthis time, the unwrinkling pressure was 9.8 kN. The formability wasevaluated according to the following criteria.

-   -   : Formable and no defect in the coating film. Completely normal        without lackluster or the like in the formed part.    -   ∘: Formable but flaw was slightly generated in the coating film.        The film formed part was changed in the color tone but free from        cracking or separation.    -   Δ: Formable but large flaw was generated in the coating film and        film cracking was observed.    -   x: Not formable.        (b) Draw-Bead Test

The steel sheet was coated with a rust-preventive oil, left in theerected state for 1 hour to 1 hour and 30 minutes, subjected to adraw-bead test under a pressing load of 9.8 kN by using a round beadingmold having a protrusion R of 4 mm and a shoulder R of 2 mm, and thenevaluated on the scratch resistance. The evaluation of the scratchresistance was performed according to the following criteria.

-   -   : No defect in the coating film. The film state was completely        normal without a lack of luster or the like in the formed part.    -   ∘: Slight generation of flaw in the coating film. The film        formed part was changed in the color tone but free from cracking        or separation.    -   Δ: Generation of large flaw in the coating film. Film cracking        was observed.    -   x: Not formable.        (4) Evaluation of Corrosion Resistance

The steel sheet after coating was formed by cylindrical deep-drawingwhile laying the coated surface on the outer side, and then a cyclecorrosion test was performed. The conditions for the cylindricaldeep-drawing were the same as in (3) above.

Also, after beading while laying the coated surface on the peak side ofthe protruded part, a cycle corrosion test was performed. The conditionsfor the beading were the same as in (3) above.

Furthermore, a cycle corrosion test was performed while leaving exposedthe cut end surface of the flat sheet.

In the cycle corrosion test, one cycle was 8 hours in total consistingof salt water spraying for 2 hours, drying for 4 hours and dampening for2 hours. The salt water spraying was performed under the conditionsaccording to JIS-K5400. The drying conditions were a temperature of 50°C. and a humidity of 30% RH or less, and the dampening conditions were atemperature of 35° C. and a humidity of 95% RH or more.

The evaluation of the corrosion resistance was performed according tothe following criteria.

(a) Cylindrical Deep-Drawn Material:

The corrosion resistance was evaluated by the cycle number until redrust was generated.

(b) Beaded Material:

The corrosion resistance was evaluated by the cycle number until redrust was generated.

(c) Flat Sheet End Face

The corrosion resistance was evaluated by the state on the end faceafter 100 cycles of CCT.

-   -   : Red rust was not generated and white rust indicating the        corrosion of the plating layer was covering the sample in an        area ratio of less than 5% of the entire area.    -   ∘: Red rust was not generated and white rust indicating the        corrosion of the plating layer was covering the sample in an        area ratio of 5% to less than 50% of the entire area.    -   Δ: Red rust was slightly generated and white rust generation        ratio was 50% or more.

x: Red rust generation ratio was 20% or more. TABLE 1 Specification ofCoated Metal Sheet Electrically Conducting Particles Mode Value forNumber Distribution Mode Value for Maximum Film Base Sheet for CoatingNumber of Volume Particle Thickness, No. Kind*¹ Undercoating*² Kind*³Vol % Mode Value, μm Particles, % Distribution, μm Size, μm μm 101 EGtrivalent Cr Particle 1 12 0.50 7 18.2 23.3 9 102 EG trivalent CrParticle 1 15 0.50 7 18.2 23.3 9 103 EG trivalent Cr Particle 1 20 0.507 18.2 23.3 9 104 EG trivalent Cr Particle 1 25 0.50 7 18.2 23.3 9 105EG trivalent Cr Particle 1 30 0.50 7 18.2 23.3 9 106 EG trivalent CrParticle 1 35 0.50 7 18.2 23.3 9 107 EG trivalent Cr Particle 1 45 0.507 18.2 23.3 9 108 EG trivalent Cr Particle 1 55 0.50 7 18.2 23.3 9 109EG trivalent Cr Particle 1 60 0.50 7 18.2 23.3 9 110 EG trivalent CrParticle 1 65 0.50 7 18.2 23.3 9 111 EG trivalent Cr Particle 2 25 0.056 1.0 20.1 9 112 EG trivalent Cr Particle 3 25 0.15 6 2.0 20.2 9 113 EGtrivalent Cr Particle 4 25 0.90 7 18.9 23.8 9 114 EG trivalent CrParticle 5 25 1.85 7 29.5 38.8 9 115 EG trivalent Cr Particle 6 25 0.554 20.2 26.2 9 116 EG trivalent Cr Particle 7 25 0.55 7 22.0 28.2 9 117EG none Particle 8 25 0.60 7 19.5 28.0 9 118 EG trivalent Cr Particle 925 0.45 7 17.2 23.5 19 119 EG trivalent Cr Particle 1 25 0.50 8 18.223.3 25 120 EG trivalent Cr Particle 1 25 0.50 8 18.2 23.3 30 121 EGtrivalent Cr Particle 1 25 0.50 5 18.2 23.3 35 122 EG trivalent CrParticle 1 25 0.50 7 18.2 23.3 3 123 EG trivalent Cr Particle 1 25 0.507 18.2 23.3 1.5 124 EG Ti-based Particle 1 25 0.50 7 18.2 23.3 9treatment 1 125 EG Zr-based Particle 1 25 0.50 7 18.2 23.3 9 treatment126 ZL trivalent Cr Particle 1 25 0.50 7 18.2 23.3 9 127 ZL trivalent CrParticle 5 25 1.85 7 29.5 38.8 9 128 GA trivalent Cr Particle 1 25 0.507 18.2 23.3 9 129 GA trivalent Cr Particle 5 25 1.85 7 29.5 38.8 9 130EG trivalent Cr Particle 10 25 0.75 8 19.6 30.8 9 131 EG trivalent CrParticle 11 35 0.85 7 20.1 32.2 9*¹EG: zinc electroplated steel sheet (plating coverage: 40 g/m²)ZL: zinc-12% nickel electroplated steel sheet (plating coverage: 40g/m²)GA: alloyed hot-dip galvanized steel sheet (plating coverage: 45 g/m²)*²trivalent chromium: trivalent chromium-treated film (film coverage: 50mg/m² [in terms of chromium])titanium-based treatment 1: titanium compound-resin-silica system (filmcoverage: 100 mg/m²)zirconium-based treatment: zirconium compound-silane couplingagent-silica system (film coverage: 200 mg/m²)*³Particle 1: 76%-silicon-containing ferrosilicon particleParticle 2: 76%-silicon-containing ferrosilicon particleParticle 3: 76%-silicon-containing ferrosilicon particleParticle 4: 76%-silicon-containing ferrosilicon particleParticle 5: 76%-silicon-containing ferrosilicon particleParticle 6: 76%-silicon-containing ferrosilicon particleParticle 7: 76%-silicon-containing ferrosilicon particleParticle 8: 76%-silicon-containing ferrosilicon particleParticle 9: 45%-silicon-containing ferrosilicon particleParticle 10: iron phosphide (Fe₂P₅) particleParticle 11: zirconium powder

TABLE 2 Performance Evaluation Results Formability Corrosion ResistanceCylindrical Cycle Number of Appearance Weldability, Electric Drawing,Beading, Cylindrical Drawn Cycle Number of End Face No. dotting numberConductivity, mΩ appearance appearance Part of Beaded Part Part Remarks101 0 —^(note)) ⊙ ⊙ 250 200 ◯ Comparison 102 800 1 ⊙ ⊙ 400 350 ◯ Example103 1500 0.05 ⊙ ⊙ 450 400 ⊙ Example 104 2100 0.05 ⊙ ⊙ 450 400 ⊙ Example105 2100 0.05 ⊙ ⊙ 450 400 ⊙ Example 106 2100 0.03 ⊙ ⊙ 450 400 ⊙ Example107 2100 0.03 ◯ ◯ 400 350 ⊙ Example 108 2100 0.03 ◯ ◯ 400 350 ⊙ Example109 2100 0.02 ◯ ◯ 350 350 ⊙ Example 110 2100 0.02 Δ Δ 150 100 ⊙Comparison 111 1000 258 ⊙ ⊙ 400 350 ⊙ Comparison 112 1300 0.56 ⊙ ⊙ 450400 ⊙ Example 113 1800 0.05 ⊙ ⊙ 450 350 ⊙ Example 114 1000 0.05 Δ Δ 200150 ◯ Comparison 115 1100 0.08 ◯ ◯ 400 300 ⊙ Example 116 1300 0.05 ◯ ◯400 300 ⊙ Example 117 2100 0.03 ◯ ◯ 400 300 ⊙ Example 118 2100 0.12 ⊙ ⊙400 350 ⊙ Example 119 1300 0.98 ◯ ◯ 450 400 ⊙ Example 120 1300 1.11 ◯ ◯450 400 ⊙ Example 121 1000 1.20 ◯ ◯ 450 350 ⊙ Example 122 2300 0.05 ⊙ ⊙300 250 ◯ Example 123 2300 0.02 ◯ ◯ 250 200 ◯ Example 124 2100 0.05 ⊙ ⊙450 350 ⊙ Example 125 2100 0.05 ⊙ ⊙ 450 350 ⊙ Example 126 >3000 0.05 ⊙ ⊙650 600 ⊙ Example 127 1300 0.05 Δ Δ 400 350 ◯ Comparison 128 >3000 0.05⊙ ⊙ 600 600 ⊙ Example 129 1300 0.05 Δ Δ 250 250 ◯ Comparison 130 21000.05 ⊙ ⊙ 350 300 ◯ Example 131 2100 0.05 ⊙ ⊙ 350 300 ◯ Example^(note))—: not measurable (∞)

The results are shown in Table 2. As verified in Examples of the presentinvention, when the size distribution of the electrically conductingparticles is controlled to have a mode value of 0.05 to 1.0 μm for theparticle size distribution and the amount of the electrically conductingparticles added is controlled to from 15 to 60 vol %, good weldability,formability and corrosion resistance can be ensured. Also, when thecontent of the particles at the mode value in the number distribution iscontrolled to 5 vol % or more or the mode value for the volumedistribution is controlled to from 2 to 20 μm or when the maximumparticle size of the electrically conducting particles and the filmthickness are controlled to respective proper values, good weldability,formability and corrosion resistance can be similarly ensured.

Nos. 101, 110, 111, 114, 127 and 129 for comparison are showing cases ofusing a coated metal sheet out of the scope of the present invention. InNo. 1 where the amount of the electrically conducting particle is small,the electric conductivity cannot be obtained. In No. 110 where theamount of the electrically conducting particles is too large, theformability decreases. In No. 111 where the mode value for the numberdistribution is low, the electric conductivity decreases. In Nos. 114,127 and 129 where the mode value for the number distribution is large,the formability and corrosion resistance are decreased.

Example 2

The conditions when an electrically conducting particle orrust-preventive pigment of various types was mixed and when the resinsystem was changed are shown in Table 3. The electrically conductingparticles and rust-preventive pigment each in a predetermined amountwere mixed with a urethane-epoxy type resin, polyester-melamine typeresin, polyester-urethane type resin, acryl-polyester type resin,polyethylene terephthalate resin or high molecular polyester resin, andthe resulting mixture was coated on a metal sheet and then baked anddried. Other conditions for the production of the coated metal sheetwere the same as in Example 1. The obtained coated metal sheets wereevaluated on the weldability, formability and corrosion resistance underthe same conditions as in Example 1. TABLE 3 Specification of CoatedMetal Sheet Electrically Conducting Particles Mode Value for NumberDistribution Mode Value Base Sheet for Mode for Volume MaximumRust-Preventive Film Coating Resin, Value, Number of Distribution,Particle Pigment Thickness, No. *¹Kind *²Undercoating *³Kind *⁴Kind Vol% μm Particles, % μm Size, μm ^(*5)Kind Vol % μm 201 EG trivalent CrResin A Particle 1 25 0.50 7 18.2 23.3 — — 9 202 EG trivalent Cr Resin AParticle 12 25 0.50 7 18.2 23.3 — — 9 203 EG trivalent Cr Resin AParticle 13 25 0.50 7 18.2 23.3 — — 9 204 EG trivalent Cr Resin AParticle 14 25 0.50 7 18.2 23.3 — — 9 205 EG trivalent Cr Resin AParticle 15 25 0.50 6 18.2 23.3 — — 9 206 EG trivalent Cr Resin AParticle 16 25 0.50 6 18.2 23.3 — — 9 207 EG trivalent Cr Resin AParticle 17 25 2.55 6 18.2 23.3 — — 9 208 EG trivalent Cr Resin AParticle 1 10 0.50 7 18.2 23.3 — — 9 209 EG trivalent Cr Resin AParticle 5 25 1.85 7 29.5 38.8 — — 9 210 ZL trivalent Cr Resin AParticle 1 25 0.50 7 18.2 23.3 Pigment 1  5 9 211 ZL trivalent Cr ResinA Particle 1 25 0.50 7 18.2 23.3 Pigment 1 10 9 212 ZL trivalent CrResin A Particle 1 25 0.50 7 18.2 23.3 Pigment 1 20 9 213 ZL trivalentCr Resin A Particle 1 25 0.50 7 18.2 23.3 Pigment 1 40 9 214 ZLtrivalent Cr Resin A Particle 1 25 0.50 7 18.2 23.3 Pigment 1 60 9 215ZL trivalent Cr Resin A Particle 1 25 0.50 7 18.2 23.3 Pigment 2 10 9216 ZL trivalent Cr Resin A Particle 1 25 0.50 7 18.2 23.3 Pigment 3 109 217 ZL trivalent Cr Resin A Particle 1 65 0.50 7 18.2 23.3 Pigment 110 9 218 EG trivalent Cr Resin B Particle 1 25 0.50 7 18.2 23.3 — — 9219 EG trivalent Cr Resin C Particle 1 25 0.50 7 18.2 23.3 — — 9 220 EGtrivalent Cr Resin D Particle 1 25 0.50 7 18.2 23.3 — — 9 221 EGtrivalent Cr Resin E Particle 1 25 0.50 7 18.2 23.3 — — 9 222 EGtrivalent Cr Resin F Particle 1 25 0.50 7 18.2 23.3 — — 9*¹EG: zinc electroplated steel sheet (plating coverage: 40 g/m²)ZL: zinc-12% nickel electroplated steel sheet (plating coverage: 40g/m²)*²trivalent chromium: trivalent chromium-treated film (film coverage: 50mg/m² [in terms of chromium])*³Resin A urethane-epoxy resinResin B polyester-melamine resinResin C polyester-urethane resinResin D acryl-polyester resinResin E polyethylene terephthalate resinResin F high molecular polyester resin*⁴Particle 1: 76%-silicon-containing ferrosilicon particleParticle 5: 76%-silicon-containing ferrosilicon particleParticle 12: Particle 1 (99 vol %) + stainless steel particle (1 vol %)Particle 13: Particle 1 (97 vol %) + stainless steel particle (3 vol %)Particle 14: Particle 1 (95 vol %) + stainless steel particle (5 vol %)Particle 15: Particle 1 (90 vol %) + stainless steel particle (10 vol %)Particle 16: Particle 1 (80 vol %) + stainless steel particle (20 vol %)Particle 17: Particle 1 (70 vol %) + stainless steel particle (30 vol %)The stainless steel particle used here had, by itself, a particle sizedistribution such that the mode value for number distribution was 2.5μm, the number of particles was 10%, and the mode value for volumedistribution was 10 μm.*⁵Pigment 1: magnesium secondary phosphate (50 parts by mass) + bakedMn₂O₃.V₂O₅ (50 parts by mass)Pigment 2: a 1/1 (by mol) mixture of Ca₃(PO₄)₂ and V₂O₅Pigment 3: a 1/1 (by mol) mixture (50 parts by mass) of Ca₃(PO₄)₂ andV₂O₅ + fumed silica (50 parts by mass)

The results are shown in Table 4. In the case of adding stainless steelparticles having a large particle size, when the content of thestainless steel particles is 5 vol % or less, weldability, formabilityand corrosion resistance in good balance are obtained without decreasingthe formability. When the content of the stainless steel particles is 10vol % or more, the formability is slightly decreased. Also, when thecontent of the rust-preventive pigment is 20 vol % or less, goodcorrosion resistance can be obtained without decreasing the weldabilityand formability. Furthermore, by using a thermoplastic resin, goodweldability can be obtained.

Nos. 207 to 209 and 217 for comparison show cases of using a coatedmetal sheet out of the scope of the present invention. In No. 208, wherethe amount of the electrically conducting particles is small, theelectric conductivity cannot be obtained. In Nos. 207 and 209, where themode value for the number distribution is too large, the formability andcorrosion resistance are greatly decreased. In No. 217, where the amountof the electrically conducting particles is too large, the formabilityis greatly decreased. TABLE 4 Performance Evaluation Results FormabilityCorrosion Resistance Weldability, Electric Cylindrical Cycle NumberCycle Appearance dotting Conductivity, Drawing, Beading, of CylindricalNumber of of End No. number mΩ appearance appearance Drawn Part BeadedPart Face Part Remarks 201 1600 0.04 ⊙ ⊙ 450 400 ⊙ Example 202 1700 0.04⊙ ⊙ 450 400 ⊙ Example 203 1800 0.03 ⊙ ⊙ 400 350 ◯ Example 204 2000 0.03⊙ ⊙ 400 350 ◯ Example 205 2000 0.03 ◯ ◯ 300 250 ◯ Example 206 2000 0.03◯ ◯ 300 250 ◯ Example 207 2200 0.03 Δ Δ 200 150 ◯ Comparison 208 0—^(note)) ◯ ◯ 300 250 ◯ Comparison 209 1500 0.05 Δ Δ 200 150 ◯Comparison 210 >3000 0.05 ⊙ ⊙ 650 600 ⊙ Example 211 >3000 0.05 ⊙ ⊙ 650600 ⊙ Example 212 1500 0.15 ⊙ ⊙ 650 600 ⊙ Example 213 1100 1.2 ◯ ◯ 600550 ⊙ Example 214 1000 5.1 ◯ ◯ 400 300 ⊙ Example 215 >3000 0.05 ⊙ ⊙ 650600 ⊙ Example 216 >3000 0.05 ⊙ ⊙ 650 600 ⊙ Example 217 >3000 0.04 Δ Δ150 100 ⊙ Comparison 218 1500 0.12 ◯ ◯ 400 350 ⊙ Example 219 1500 0.13 ⊙⊙ 450 400 ⊙ Example 220 1400 0.15 ◯ ◯ 400 350 ⊙ Example 221 1800 0.1 ⊙ ⊙450 400 ⊙ Example 222 1800 0.11 ⊙ ⊙ 450 400 ⊙ Example^(note))—: not measurable (∞)

Example 3

Metal sheets coated with a urethane-epoxy type resin film containing anelectrically conducting particle or other particle controlled in theparticle size distribution were evaluated on the aptitude as a fuel tankmaterial and the results are shown in Table 5. In addition to the itemsof the performance evaluation in Example 1 except for the corrosionresistance of the end face, the following seam weldability test andcorrosion resistance test simulating the inner surface side of tank wereperformed.

(5) Seam Weldability

Seam welding of 10 m was performed with 2-on/1-off electrification at awelding current of 11 kA and an applied pressure of 4.9 kN by using anelectrode ring having a tip R of 6 mm and a diameter of 250 mm.Thereafter, a specimen according to JIS-Z-3141 was prepared and testedon the leakage.

-   -   : No leakage.    -   ∘: No leakage but the welded part surface was slightly        roughened.    -   Δ: No leakage but defects such as cracking were generated on the        welded part surface.    -   x: Leakage was generated.        (6) Inner Surface Corrosion Resistance

The corrosion resistance against gasoline was evaluated. As for themethod therefor, a test solution was poured in a sample deep-drawn intoa flat-bottom cylinder having a flange width of 20 mm, a diameter of 50mm and a depth of 25 mm by a hydraulic forming tester, and a glass coverwas secured thereon through a silicon rubber-made ring. After this test,the corroded state was observed by eye.

(Test Conditions)

Test Solution:gasoline+distilled water (10%)+formic acid (200 ppm)Test period: left standing at 40° C. for 3 months.(Criteria of Evaluation)

-   -   : No change.    -   ∘: White rust generation ratio was 0.1% or less.    -   Δ: Red rust generation ratio was 5% or less or white rust        generation ratio was from 0.1 to 50%.

x: Red rust generation ratio was exceeding 5% or conspicuous white rust.TABLE 5 Specification of Coated Metal Sheet Electrically ConductingParticles Base Sheet for Mode Value for Number Mode Value CoatingDistribution for Volume Maximum Rust-Preventive Film *²Under- ModeNumber of Distribution, Particle Pigment Thickness No. *¹Kind coating*³Kind Vol % Value, μm Particles, % μm Size, μm *⁴Kind Vol % μm 301 ZLtrivalent Cr Particle 1 12 0.50 7 18.2 23.3 — — 9 302 ZL trivalent CrParticle 1 25 0.50 7 18.2 23.3 Pigment 1 10 9 303 ZL trivalent CrParticle 18 25 0.55 4 20.2 26.2 Pigment 1 10 9 304 ZL trivalent CrParticle 19 25 0.55 7 22.0 28.2 Pigment 1 10 9 305 ZL trivalent CrParticle 20 25 0.90 7 18.9 23.8 Pigment 1 10 9 306 ZL trivalent CrParticle 21 25 1.85 7 29.5 38.8 Pigment 1 10 9 307 ZL Zr-based Particle22 25 0.5 6 18 23 Pigment 2 10 22 treatment 308 ZL Zr-based Particle 2325 0.5 7 18 23 Pigment 3 10 9 treatment 309 Sn—Zn trivalent Cr Particle1 12 0.5 7 18 23 — — 9 310 Sn—Zn trivalent Cr Particle 1 25 0.5 7 18 23Pigment 1 10 9 311 Sn—Zn trivalent Cr Particle 18 25 0.55 4 20.2 26.2Pigment 1 10 9 312 Sn—Zn trivalent Cr Particle 19 25 0.55 7 22.0 28.2Pigment 1 10 9 313 Sn—Zn trivalent Cr Particle 20 25 0.90 7 18.9 23.8Pigment 1 10 9 314 Sn—Zn trivalent Cr Particle 21 25 1.85 7 29.5 38.8Pigment 1 10 9 315 Sn—Zn Ti-based Particle 22 25 0.50 7 18.2 23.3Pigment 2 10 24 treatment 2 316 Sn—Zn Ti-based Particle 23 25 0.50 618.2 23.3 Pigment 3 10 9 treatment 2 317 ZL trivalent Cr Particle 10 650.75 8 19.6 30.8 Pigment 1 10 9 318 ZL trivalent Cr Particle 11 25 0.857 20.1 32.2 Pigment 1 10 9*¹ZL: zinc-12% nickel electroplated steel sheet (plating coverage: 40g/m²)Sn-hot-dip tin-8% zinc plated steel sheetzinc: (plating coverage: 40 g/m²)*²trivalent chromium: trivalent chromium-treated film (film coverage: 50mg/m² [in terms of chromium])titanium-based treatment 2: titanium compound-resin-phosphoric acid(film coverage: 300 mg/m²)zirconium-based treatment: zirconium compound-silane couplingagent-silica system (film coverage: 200 mg/m²)*³Particle 1: 76%-silicon-containing ferrosilicon particleParticle 10: iron phosphide (Fe₂P₅) particleParticle 11: zinc powderParticle 18: Particle 6 (99 vol %) + stainless steel particle (1 vol %)Particle 19: Particle 7 (99 vol %) + stainless steel particle (1 vol %)Particle 20: Particle 4 (99 vol %) + stainless steel particle (1 vol %)Particle 21: Particle 5 (99 vol %) + stainless steel particle (1 vol %)Particle 22: Particle 1 (99 vol %) + stainless steel particle (1 vol %)Particle 23: Particle 1 (90 vol %) + stainless steel particle (10 vol %)*⁴Pigment 1: magnesium secondary phosphate (50 parts by mass) + bakedMn₂O₃.V₂O₅ (50 parts by mass)Pigment 2: a 1/1 (by mol) mixture of Ca₃(PO₄)₂ and V₂O₅Pigment 3: a 1/1 (by mol) mixture (50 parts by mass) of Ca₃(PO₄)₂ andV₂O₅ + fumed silica (50 parts by mass)

The results are shown in Table 6. It is seen that the coated metal sheetwhere the electrically conducting particles or other particles arecontrolled to a proper size distribution and a proper content, isexcellent in the weldability, formability and corrosion resistance andalso suited as a fuel tank material.

Nos. 301, 306, 309 and 314 for comparison are showing coated metalsheets out of the scope of the present invention. In Nos. 301 and 309where the amount of the electrically conducting particles is small, theweldability is not good. In Nos. 306 and 314 where the mode value forthe number distribution is large, the formability and corrosionresistance are bad. TABLE 6 Performance Evaluation Results CorrosionResistance Formability Cycle Cycle Inner Weldability, ElectricCylindrical Number of Number of Surface dotting Conductivity, Drawing,Beading, Cylindrical Beaded Seam Corrosion No. number mΩ appearanceappearance Drawn Part Part Weldability Resistance Remarks 301 0—^(note)) ⊙ ⊙ 300 250 X ◯ Comparison 302 2100 0.05 ⊙ ⊙ 500 450 ⊙ ◯Example 303 1300 0.08 ◯ ◯ 400 300 ◯ ◯ Example 304 1300 0.05 ◯ ◯ 450 350◯ ◯ Example 305 2100 0.03 ⊙ ⊙ 500 400 ⊙ ◯ Example 306 1300 0.05 Δ Δ 150100 ◯ ◯ Comparison 307 1000 1.12 ⊙ ⊙ 450 400 ◯ ◯ Example 308 2500 0.03 ◯◯ 200 150 ⊙ ◯ Example 309 0 —^(note)) ⊙ ⊙ 350 300 X ⊙ Comparison 310 5000.05 ⊙ ⊙ 600 500 ⊙ ⊙ Example 311 400 0.08 ◯ ◯ 500 400 ◯ ⊙ Example 312400 0.05 ◯ ◯ 500 400 ◯ ⊙ Example 313 500 0.03 ⊙ ⊙ 600 500 ⊙ ⊙ Example314 400 0.05 Δ Δ 150 100 ◯ ⊙ Comparison 315 350 1.2  ⊙ ⊙ 450 400 ◯ ⊙Example 316 500 0.03 ◯ ◯ 250 200 ⊙ ⊙ Example 317 2100 0.05 ⊙ ⊙ 350 300 ⊙◯ Example 318 2100 0.05 ⊙ ⊙ 350 300 ⊙ ◯ Example^(note))—: not measurable (∞)

Example 4

Various electrically conducting particles were prepared and ground by aginder, or classified according to the conditions, to produce particleshaving various size distributions. A predetermined amount of eachelectrically conducting particle was mixed with a urethane-epoxy typeresin and the obtained mixture was coated on a metal sheet, then bakedand dried. In some Samples, the organic film was coated after anundercoating film was applied to the metal sheet. The conditions thereofare shown in Table 7. At this time, the drying condition was 210° C. asa peak metal temperature. The thus-obtained coated metal sheets weresubjected to evaluations of weldability, formability and corrosionresistance under the following conditions. TABLE 7 Specification ofCoated Metal Sheet Electrically Conducting Particles Mode Value forNumber Distribution Mode Value for Maximum Film Base Sheet for CoatingNumber of Volume Particle Thickness, No. Kind*¹ Undercoating*² Kind*³Vol % Mode Value, μm Particles, % Distribution, μm Size, μm μm 401 EGtrivalent Cr Particle 1 10 0.40 7 18.5 23.8 10 402 EG trivalent CrParticle 1 15 0.40 7 18.5 23.8 10 403 EG trivalent Cr Particle 1 20 0.407 18.5 23.8 10 404 EG trivalent Cr Particle 1 25 0.40 7 18.5 23.8 10 405EG trivalent Cr Particle 1 30 0.40 7 18.5 23.8 10 406 EG trivalent CrParticle 1 35 0.40 7 18.5 23.8 10 407 EG trivalent Cr Particle 1 45 0.407 18.5 23.8 10 408 EG trivalent Cr Particle 1 55 0.40 7 18.5 23.8 10 409EG trivalent Cr Particle 1 60 0.40 7 18.5 23.8 10 410 EG trivalent CrParticle 1 65 0.40 7 18.5 23.8 10 411 EG trivalent Cr Particle 2 300.025 6 1.3 20.5 9 412 EG trivalent Cr Particle 3 30 0.05 6 3.5 20.6 9413 EG trivalent Cr Particle 4 30 0.05 6 2.1 20.0 9 414 EG trivalent CrParticle 5 30 0.15 6 3.3 20.4 9 415 EG trivalent Cr Particle 6 30 0.65 718.9 23.6 9 416 EG trivalent Cr Particle 7 30 0.95 7 23.3 29.6 9 417 EGtrivalent Cr Particle 8 30 1.20 7 30.2 36.6 9 418 EG trivalent CrParticle 9 30 1.55 7 35.9 43.3 9 419 EG trivalent Cr Particle 10 30 2.008 45.0 55.2 9 420 EG none Particle 11 30 1.95 8 22.8 30.3 10 421 EG noneParticle 12 30 0.60 5 27.1 37.0 10 422 EG trivalent Cr Particle 13 300.55 7 19.3 29.0 10 423 EG trivalent Cr Particle 14 30 0.50 7 18.4 23.615 424 EG trivalent Cr Particle 1 30 0.40 7 18.5 23.8 20 425 EGtrivalent Cr Particle 1 30 0.40 7 18.5 23.8 25 426 EG trivalent CrParticle 1 30 0.40 7 18.5 23.8 30 427 EG trivalent Cr Particle 1 30 0.407 18.5 23.8 3 428 EG trivalent Cr Particle 1 30 0.40 7 18.5 23.8 1 429EG Ti-based Particle 1 30 0.40 7 18.5 23.8 9 treatment 1 430 EG Zr-basedParticle 1 30 0.40 7 18.5 23.8 9 treatment 431 ZL trivalent Cr Particle1 30 0.40 7 18.5 23.8 9 432 ZL trivalent Cr Particle 8 30 1.20 7 30.236.6 9 433 GA trivalent Cr Particle 1 30 0.40 7 18.5 23.8 9 434 GAtrivalent Cr Particle 8 30 1.20 7 30.2 36.6 9 435 EG trivalent CrParticle 15 30 0.70 7 20.2 29.5 10 436 EG trivalent Cr Particle 16 350.80 7 22.3 31.3 10*¹EG: zinc electroplated steel sheet (plating coverage: 40 g/m²)ZL: zinc-12% nickel electroplated steel sheet (plating coverage: 40g/m²)GA: alloyed hot-dip galvanized steel sheet (plating coverage: 45 g/m²)*²trivalent chromium: trivalent chromium-treated film (film coverage: 50mg/m² [in terms of chromium])titaniuim-based treatment 1: titaniuim compound-resin-silica system(film coverage: 100 mg/m²)zirconium-based treatment: zirconium compound-silane couplingagent-silica system (film coverage: 200 mg/m²)*³Particle 1: 76%-silicon-containing ferrosilicon particleParticle 2: 76%-silicon-containing ferrosilicon particleParticle 3: 76%-silicon-containing ferrosilicon particleParticle 4: 76%-silicon-containing ferrosilicon particleParticle 5: 76%-silicon-containing ferrosilicon particleParticle 6: 76%-silicon-containing ferrosilicon particleParticle 7: 76%-silicon-containing ferrosilicon particleParticle 8: 76%-silicon-containing ferrosilicon particleParticle 9: 76%-silicon-containing ferrosilicon particleParticle 10: 76%-silicon-containing ferrosilicon particleParticle 11: 76%-silicon-containing ferrosilicon particleParticle 12: 76%-silicon-containing ferrosilicon particleParticle 13: 76%-silicon-containing ferrosilicon particleParticle 14: 45%-silicon-containing ferrosilicon particleParticle 15: iron phosphide (Fe₂P₅) particleParticle 16: zinc powder

The results are shown in Table 8. As verified in Examples of the presentinvention, when the size distribution of the electrically conductingparticles is controlled to have a relationship satisfying apredetermined correlation expression among the mode value Mn for thenumber distribution every each particle size of the electricallyconducting particles, the mode value Mv in the volume distribution inrelation to particle size of the electrically conducting particle andthe thickness H of the coat layer and at the same time, the content ofthe electrically conducting particle in the coat layer is from 15 to 60vol %, good weldability, formability and corrosion resistance can beensured. Also, when the film thickness is controlled to a proper value,good weldability, formability and corrosion resistance can be similarlyensured.

Nos. 401, 410, 411, 412, 419, 420 and 428 for comparison show cases ofusing a coated metal sheet out of the scope of the present invention. InNo. 1 where the amount of the electrically conducting particle is small,the electric conductivity cannot be obtained. In No. 410 where theamount of the electrically conducting particles is too large, theformability decreases. In No. 412 where Mv/Mn is less than 12, theweldability decreases. In No. 419 where Mv/Mn exceeds 50, the corrosionresistance and formability are decreased. In No. 411 where the thicknessH of the coat layer exceeds 200 Mn, the weldability decreases. In No.420 where the thickness H of the coat layer is less than 5 Mn, thecorrosion resistance and formability are decreased. In No. 428 where Mvexceeds 10H, the corrosion resistance and formability are decreased.TABLE 8 Performance Evaluation Results Formability Corrosion ResistanceWeldability, Electric Cylindrical Cycle Number Cycle Appearance dottingConductivity, Drawing, Beading, of Cylindrical Number of of End No.number mΩ appearance appearance Drawn Part Beaded Part Face Part Remarks401 0 —^(note)) ⊙ ⊙ 250 200 Δ Comparison 402 800 1.2 ⊙ ⊙ 400 350 ◯Example 403 1400 0.05 ⊙ ⊙ 450 400 ⊙ Example 404 2000 0.05 ⊙ ⊙ 450 400 ⊙Example 405 2000 0.05 ⊙ ⊙ 450 400 ⊙ Example 406 2000 0.03 ⊙ ⊙ 450 400 ⊙Example 407 1900 0.03 ◯ ◯ 400 400 ◯ Example 408 1900 0.03 ◯ ◯ 400 350 ◯Example 409 1900 0.02 ◯ ◯ 400 350 ◯ Example 410 1900 0.02 Δ Δ 150 100 ⊙Comparison 411 150 165 ◯ ◯ 350 300 ⊙ Comparison 412 1300 0.85 Δ Δ 200100 Δ Comparison 413 1000 0.64 ⊙ ⊙ 450 400 ⊙ Example 414 1100 0.33 ⊙ ⊙450 400 ⊙ Example 415 1600 0.05 ⊙ ⊙ 450 350 ⊙ Example 416 1600 0.05 ⊙ ⊙450 350 ⊙ Example 417 1200 0.05 ◯ ◯ 250 200 ◯ Example 418 1200 0.05 ◯ ◯250 200 ◯ Example 419 1200 0.03 Δ Δ 200 150 ◯ Comparison 420 300 0.9 ◯ ◯250 200 ◯ Comparison 421 1700 0.08 ◯ ◯ 400 350 ⊙ Example 422 1900 0.03 ⊙⊙ 450 400 ⊙ Example 423 2300 0.05 ⊙ ⊙ 400 350 ⊙ Example 424 1200 0.05 ⊙⊙ 450 400 ⊙ Example 425 1100 0.05 ⊙ ⊙ 450 400 ⊙ Example 426 2300 0.05 ⊙◯ 400 350 ⊙ Example 427 2300 0.02 ⊙ ⊙ 300 250 ◯ Example 428 2300 0.02 ΔΔ 150 100 X Comparison 429 2100 0.05 ⊙ ⊙ 450 350 ⊙ Example 430 2100 0.05⊙ ⊙ 450 350 ⊙ Example 431 >3000 0.05 ⊙ ⊙ 650 600 ⊙ Example 432 1800 0.05◯ ◯ 500 450 ◯ Example 433 >3000 0.05 ⊙ ⊙ 600 600 ⊙ Example 434 1800 0.05◯ ◯ 450 400 ◯ Example 435 2100 0.05 ⊙ ⊙ 350 300 ◯ Example 436 2100 0.05⊙ ⊙ 350 300 ◯ Example^(note))—: not measurable (∞)

Example 5

The conditions when electrically conducting particles or rust-preventivepigment of various types were mixed and when the resin system waschanged are shown in Table 9. The electrically conducting particle andrust-preventive pigment each in a predetermined amount were mixed with aurethane-epoxy type resin, polyester-melamine type resin,polyester-urethane type resin, acryl-polyester type resin, polyethyleneterephthalate resin or polyolefin resin, and the resulting mixture wascoated on a metal sheet and then baked•dried. Other conditions for theproduction of the coated metal sheet were the same as in Example 1. Theobtained coated metal sheets were evaluated on the weldability,formability and corrosion resistance under the same conditions as inExample 1. TABLE 9 Specification of Coated Metal Sheet ElectricallyConducting Particles Mode Value for Number Distribution Mode Value BaseSheet for Mode for Volume Maximum Rust-Preventive Film Coating Resin,Value, Number of Distribution, Particle Pigment Thickness, No. *¹Kind*²Undercoating *³Kind *⁴Kind Vol % μm Particles, % μm Size, μm ^(*5)KindVol % μm 501 EG trivalent Cr Resin A Particle 1 25 0.40 7 18.5 23.8 — —10 502 EG trivalent Cr Resin A Particle 17 10 0.40 7 18.5 23.8 — — 10503 EG trivalent Cr Resin A Particle 18 25 2.00 7 45.0 55.2 — — 10 504EG trivalent Cr Resin A Particle 19 25 0.40 7 18.5 23.8 — — 10 505 EGtrivalent Cr Resin A Particle 20 25 0.40 7 18.5 23.8 — — 10 506 EGtrivalent Cr Resin A Particle 21 25 0.40 6 18.5 23.8 — — 10 507 EGtrivalent Cr Resin A Particle 22 65 0.40 6 18.5 23.8 — — 10 508 ZLtrivalent Cr Resin A Particle 17 25 0.40 7 18.5 23.8 Pigment 1 5 10 509ZL trivalent Cr Resin A Particle 17 25 0.40 7 18.5 34.8 Pigment 1 10 10510 ZL trivalent Cr Resin A Particle 17 25 0.40 7 18.5 23.8 Pigment 1 2010 511 ZL trivalent Cr Resin A Particle 17 25 0.40 7 18.5 23.8 Pigment 140 10 512 ZL trivalent Cr Resin A Particle 17 25 0.40 7 18.5 23.8Pigment 1 60 10 513 ZL trivalent Cr Resin A Particle 17 25 0.40 7 18.523.8 Pigment 2 10 10 514 ZL trivalent Cr Resin A Particle 17 25 0.40 718.5 23.8 Pigment 3 10 10 515 EG trivalent Cr Resin B Particle 17 250.40 7 18.5 23.8 — — 10 516 EG trivalent Cr Resin C Particle 17 25 0.407 18.5 23.8 — — 10 517 EG trivalent Cr Resin D Particle 17 25 0.40 718.5 23.8 — — 10 518 EG trivalent Cr Resin E Particle 17 25 0.40 7 18.523.8 — — 10 519 EG trivalent Cr Resin F Particle 17 25 0.40 7 18.5 23.8— — 10*¹EG: zinc electroplated steel sheet (plating coverage: 40 g/m²)ZL: zinc-12% nickel electroplated steel sheet (plating coverage: 40g/m²)*²trivalent chromium: trivalent chromium-treated film (film coverage: 50mg/m² [in terms of chromium])*³Resin A urethane-epoxy resinResin B polyester-melamine resinResin C polyester-urethane resinResin D acryl-polyester resinResin E polyethylene terephthalate resinResin F polyolefin resin*⁴Particle 1: 76%-silicon-containing ferrosilicon particleParticle 17: Particle 1 (99 vol %) + stainless steel particle (1 vol %)Particle 18: Particle 10 (99 vol %) + stainless steel particle (1 vol %)Particle 19: Particle 1 (97 vol %) + stainless steel particle (3 vol %)Particle 20: Particle 1 (95 vol %) + stainless steel particle (5 vol %)Particle 21: Particle 1 (90 vol %) + stainless steel particle (10 vol %)Particle 22: Particle 1 (80 vol %) + stainless steel particle (20 vol %)The stainless steel particle used here had, by itself, a particle sizedistribution such that the mode value for number distribution was 2.5μm, the number of particles was 10%, the mode value for volumedistribution s 7 μm, and the maximum particle size was 10 μm.*⁵Pigment 1: magnesium secondary phosphate (50 parts by mass) + bakedMn₂O₃.V₂O₅ (50 parts by mass)Pigment 2: a 1/1 (by mol) mixture of Ca₃(PO₄)₂ and V₂O₅Pigment 3: a 1/1 (by mol) mixture (50 parts by mass) of Ca₃(PO₄)₂ andV₂O₅ + fumed silica (50 parts by mass)

The results are shown in Table 10. In the case of adding the stainlesssteel particles having a large particle size, when the content of thestainless steel particle is 5 vol % or less, weldability, formabilityand corrosion resistance in good balance are obtained without decreasingthe formability. When the content of the stainless steel particle is 10vol % or more, the formability is slightly decreased. Also, when thecontent of the rust-preventive pigment is 20 vol % or less, goodcorrosion resistance can be obtained without decreasing the weldabilityand formability. Furthermore, by using a thermoplastic resin, goodweldability can be obtained.

Nos. 502, 503 and 507 for comparison are showing cases of using a coatedmetal sheet out of the scope of the present invention. In No. 502 wherethe amount of the electrically conducting particles is too small, theelectric conductivity cannot be obtained. In No. 503 where H is lessthan 5 Mn, the formability and corrosion resistance are decreased. InNo. 507 where the amount of the electrically conducting particlesexceeds 60 vol %, the formability is bad. TABLE 10 PerformanceEvaluation Results Formability Corrosion Resistance Weldability,Electric Cylindrical Cycle Number Cycle Appearance dotting Conductivity,Drawing, Beading, of Cylindrical Number of of End No. number mΩappearance appearance Drawn Part Beaded Part Face Part Remarks 501 15000.04 ⊙ ⊙ 400 400 ⊙ Example 502 0 —^(note)) ⊙ ⊙ 300 300 ◯ Comparison 5031200 0.03 Δ Δ 200 150 ◯ Comparison 504 1500 0.04 ⊙ ⊙ 400 400 ⊙ Example505 1700 0.03 ⊙ ⊙ 400 350 ⊙ Example 506 1800 0.05 ◯ ◯ 300 250 ◯ Example507 1800 0.05 Δ Δ 150 100 ◯ Comparison 508 2500 0.05 ⊙ ⊙ 600 550 ⊙Example 509 2500 0.05 ⊙ ⊙ 600 550 ⊙ Example 510 2400 0.03 ⊙ ⊙ 600 550 ⊙Example 511 1500 0.23 ◯ ◯ 550 500 ⊙ Example 512 1100 1.9  Δ Δ 400 300 ⊙Example 513 2800 0.06 ⊙ ⊙ 650 600 ⊙ Example 514 2800 0.06 ⊙ ⊙ 650 600 ⊙Example 515 1500 0.12 ◯ ◯ 400 350 ⊙ Example 516 1500 0.13 ⊙ ⊙ 450 400 ⊙Example 517 1400 0.15 ◯ ◯ 400 350 ⊙ Example 518 1800 0.10 ⊙ ⊙ 450 400 ⊙Example 519 1800 0.11 ⊙ ⊙ 450 400 ⊙ Example^(note))—: not measurable (∞)

Example 6

Metal sheets coated with a urethane-epoxy type resin film containingelectrically conducting particles or other particles controlled in theparticle size distribution were evaluated on the aptitude as a fuel tankmaterial and the results are shown in Table 11. In addition to the itemsof the performance evaluation in Example 1 except for the corrosionresistance of the end face, the seam weldability test and corrosionresistance test simulating the inner surface side of tank described inExample 3 were performed. TABLE 11 Specification of Coated Metal SheetElectrically Conducting Particles Mode value for Number DistributionMode Value Mode for Volume Maximum Rust-Preventive Film Base Sheet forCoating Value, Number of Distribution, Particle Pigment Thickness, No.*¹Kind *²Undercoating *³Kind Vol % μm Particles, % μm Size, μm *⁴KindVol % μm 601 ZL trivalent Cr Particle 1 10 0.40 7 18.5 23.8 — — 10 602ZL trivalent Cr Particle 23 25 0.40 7 18.5 23.8 Pigment 1 10 10 603 ZLtrivalent Cr Particle 23 35 0.40 7 18.5 23.8 Pigment 1 10 10 604 ZLtrivalent Cr Particle 24 25 0.15 7 3.3 20.4 Pigment 1 10 10 605 ZLtrivalent Cr Particle 25 25 0.95 7 23.3 29.6 Pigment 1 10 10 606 ZLtrivalent Cr Particle 26 25 2.00 7 45.0 55.2 Pigment 1 10 10 607 ZLZr-based Particle 23 25 0.40 7 18.5 23.8 Pigment 1 10 10 treatment 608ZL Zr-based Particle 23 25 0.40 7 18.5 23.8 Pigment 2 10 25 treatment609 ZL Zr-based Particle 23 25 0.40 7 18.5 23.8 Pigment 3 10 10treatment 610 ZL trivalent Cr Particle 15 25 0.70 7 20.2 29.5 Pigment 110 10 611 ZL trivalent Cr Particle 16 35 0.80 7 22.3 31.3 Pigment 1 1010 612 Sn—Zn trivalent Cr Particle 1 10 0.40 7 18.5 23.8 — — 10 613Sn—Zn trivalent Cr Particle 23 25 0.40 7 18.5 23.8 Pigment 1 10 10 614Sn—Zn trivalent Cr Particle 23 35 0.40 7 18.5 23.8 Pigment 1 10 10 615Sn—Zn trivalent Cr Particle 23 45 0.40 7 18.5 23.8 Pigment 1 10 10 616Sn—Zn trivalent Cr Particle 23 60 0.40 7 18.5 23.8 Pigment 1 10 10 617Sn—Zn trivalent Cr Particle 24 25 0.15 7 3.3 20.4 Pigment 1 10 10 618Sn—Zn trivalent Cr Particle 25 25 0.95 7 23.3 29.6 Pigment 1 10 10 619Sn—Zn trivalent Cr Particle 27 25 1.55 7 35.9 43.3 Pigment 1 10 10 620Sn—Zn trivalent Cr Particle 26 25 2.00 7 45.0 55.2 Pigment 1 10 10 621Sn—Zn Ti-based Particle 23 25 0.40 7 18.5 23.8 Pigment 1 10 10 treatment2 622 Sn—Zn Ti-based Particle 23 25 0.40 7 18.5 23.8 Pigment 2 10 25treatment 2 623 Sn—Zn Ti-based Particle 23 25 0.40 7 18.5 23.8 Pigment 310 10 treatment 2*¹ZL: zinc-12% nickel electroplated steel sheet (plating coverage: 40g/m²)Sn-hot-dip tin-8% zinc plated steel sheetzinc: (plating coverage: 40 g/m²)*²trivalent chromium: trivalent chromium-treated film (film coverage: 50mg/m² [in terms of chromium])titanium-based treatment 2: titanium compound-resin-phosphoric acid(film coverage: 300 mg/m²)zirconium-based treatment: zirconium compound-silane couplingagent-silica system (film coverage: 200 mg/m²)*³Particle 1: 76%-silicon-containing ferrosilicon particleParticle 15: iron phosphide (Fe₂P₅) particleParticle 16: zinc powderParticle 23: Particle 1 (99 vol %) + stainless steel particle (1 vol %)Particle 24: Particle 5 (99 vol %) + stainless steel particle (1 vol %)Particle 25: Particle 7 (99 vol %) + stainless steel particle (1 vol %)Particle 26: Particle 10 (99 vol %) + stainless steel particle (1 vol %)Particle 27: Particle 9 (99 vol %) + stainless steel particle (1 vol %)*⁴Pigment 1: magnesium secondary phosphate (50 parts by mass) + bakedMn₂O₃.V₂O₅ (50 parts by mass)Pigment 2: a 1/1 (by mol) mixture of Ca₃(PO₄)₂ and V₂O₅Pigment 3: a 1/1 (by mol) mixture (50 parts by mass) of Ca₃(PO₄)₂ andV₂O₅ + fumed silica (50 parts by mass)

The results are shown in Table 12. It is seen that when the sizedistribution of the electrically conducting particle is controlled tohave a relationship satisfying a predetermined correlation expressionamong the mode value Mn for the number distribution every each particlesize of the electrically conducting particles, the mode value Mv at thevolume distribution in relation to particle size of the electricallyconducting particles and the thickness H of the coat layer, the coatedsteel sheet is excellent in the weldability, formability and corrosionresistance and also suited as a fuel tank material.

Nos. 601, 606, 612, 616 and 620 for comparison show coated metal sheetsout of the scope of the present invention. In Nos. 601 and 612 where theamount of the electrically conducting particle is small, the weldabilityis poor. In Nos. 606 and 620 where the mode value Mn for the numberdistribution of the electrically conducting particle is large and H isless than 5 Mn, the formability and corrosion resistance are bad. In No.616 where the amount of the electrically conducting particles is toolarge, the formability decreases. TABLE 12 Performance EvaluationResults Corrosion Resistance Formability Cycle Cycle Inner Weldability,Electric Cylindrical Number of Number of Surface dotting Conductivity,Drawing, Beading, Cylindrical Beaded Seam Corrision No. number mΩappearance appearance Drawn Part Part Weldability Resistance Remarks 6010 —^(note)) ⊙ ⊙ 300 250 X ◯ Comparison 602 2000 0.06 ⊙ ⊙ 550 450 ⊙ ◯Example 603 1300 0.08 ⊙ ⊙ 550 400 ◯ ◯ Example 604 1300 0.05 ⊙ ⊙ 500 350◯ ◯ Example 605 2000 0.04 ⊙ ⊙ 450 350 ⊙ ◯ Example 606 1100 0.06 ⊙ ⊙ 250200 Δ ◯ Comparison 607 2000 0.06 ⊙ ⊙ 550 450 ⊙ ◯ Example 608 1400 0.05 ⊙⊙ 550 450 ◯ ◯ Example 609 2400 0.03 ◯ ◯ 250 200 ⊙ ◯ Example 610 20000.06 ⊙ ⊙ 500 400 ⊙ ◯ Example 611 2000 0.07 ⊙ ⊙ 500 400 ⊙ ⊙ Example 612 0—^(note)) ⊙ ⊙ 400 300 X ⊙ Comparison 613 400 0.07 ⊙ ⊙ 650 500 ⊙ ⊙Example 614 500 0.07 ⊙ ⊙ 650 500 ⊙ ⊙ Example 615 500 0.07 ◯ ◯ 650 500 ⊙⊙ Example 616 500 0.08 Δ Δ 400 350 ⊙ ⊙ Comparison 617 450 0.06 ⊙ ⊙ 650500 ◯ ⊙ Example 618 500 0.05 ⊙ ⊙ 550 400 ⊙ ⊙ Example 619 450 0.08 ◯ ◯350 250 ◯ ⊙ Example 620 400 0.08 Δ Δ 350 250 Δ ⊙ Comparison 621 500 0.07⊙ ⊙ 650 500 ⊙ ⊙ Example 622 450 0.07 ⊙ ⊙ 500 400 ◯ ⊙ Example 623 5000.05 ◯ ◯ 250 200 ⊙ ⊙ Example^(note))—: not measurable (∞)

Example 7

First, in the following Nos. 1 to 46, the contents of the coatingmaterial and undercoating agent where a polyol, a resin having mixedtherein a blocked product, and an epoxy resin or an adduct thereof areblended with a rust inhibitor and an electrically conducting particleare described below. Next, Examples of the present invention andComparative Examples are described.

The contents of Examples and Comparative Examples are shown in Tables 20to 23. In Examples and Comparative Examples, the electrically conductingparticle of Nos. 30 to 38 shown in Table 17 and/or the rust inhibitor ofNos. 25 to 29 in Table 18 were blended•dispersed at the blending ratioshown in Tables 20 to 23 in a resin where the polyol of Nos. 1 to 5 inTable 13, the blocked product of Nos. 6 to 8 in Table 14 and/or theepoxy resin or an adduct thereof of Nos. 9 to 11 in Table 15 wereblended at the ratio of Nos. 12 to 24 in Table 16, and the obtainedcoating material was applied to a plated steel sheet subjected to anundercoating treatment, and then heated to give a peak steel temperatureof 220° C., whereby the organic film was formed. The contents of theundercoating treatment are shown in Table 19. The plated steel sheetused had a thickness of 0.8 mm and the construction material used forthe steel sheet was free from cracking even when bent at 180° withintervention of a spacer having a thickness of 0.8 mm.

As for the performance evaluation in Examples of the present inventionand Comparative Examples, a formability test, a test on corrosionresistance after cup drawing, and a weldability test were performed.Also, the presence or absence of hexavalent chromium and trivalentchromium was examined.

(1) Formability Test

The sheet after coating was bent at 180° C. with intervention of aspacer having a thickness of 0.8 mm, and the film state in the bent partwas observed by a magnifier at a magnification of 10 times.

In the evaluation of the film state, the sample was rated 4 when theformed part was completely normal without lackluster or the like in theformed part, rated 3 when the formed part was slightly changed in thecolor tone but had no cracking or separation, rated 2 when slightlycracked, and rated 1 when cracking was observed even without using amagnifier.

(2) Test on Corrosion Resistance after Cup Drawing

The steel sheet after coating was formed by cylindrical cup drawing suchthat the coated surface came to the outer side, and then subjected to acycle corrosion test. In the cylindrical cup drawing, the steel sheetwas coated with a rust-preventive oil, left in the erected state for 1hour to 1 hour and 30 minutes, and then drawn at a drawing ratio of 1.8by using a metal mold having a punch diameter of 50 mm, a punch shoulderR of 3 mm, a die diameter of 52 mm and a die shoulder R of 3 mm.

In the cycle corrosion test, one cycle was 8 hours in total consistingof salt water spraying for 2 hours, drying for 2 hours and dampening for2 hours. The salt water spraying was performed under the conditionsaccording to JIS-K5400. The drying conditions were a temperature of 50°C. and a humidity of 30% RH or less, and the dampening conditions were atemperature of 35° C. and a humidity of 95% RH or more.

In the evaluation of the corrosion resistance, the sample was rated 4when red rust indicating the decrease in the thickness of the steelsheet was not generated and white rust indicating the corrosion of theplating layer was covering the sample in an area ratio of 50% or less ofthe entire area, rated 3 when red rust indicating the decrease in thethickness of the steel sheet was not generated even after 300 cycles,rated 2 when red rust was not observed after 100 cycles but observedafter 300 cycles, and rated 1 when red rust was observed after 100cycles.

(3) Weldability Test

Two coated steel sheets were combined and subjected to a continuous spotwelding test and the dotting number where continuous welding could beperformed was evaluated. The welding conditions were such that theelectrode tip diameter was 4 mm, the applied pressure was 300 kg and theelectrification time in one welding operation was 0.2 seconds. Thewelding current value was determined by the following procedure. Thatis, the current value was gradually increased from 3 kA at every 0.2 kAunder the conditions that the electrode tip diameter was 4 mm, theapplied pressure was 300 kg and the electrification time in one weldingoperation was 0.2 seconds, and (the current value when the nuggetdiameter first exceeded 3.6 mm+the current value when the coated steelsheet after welding was first strongly welded to the electrode)÷2 wasdetermined as the welding current value in the continuous welding test.

In the evaluation of continuous weldability, the sample was rated 3 whena nugget diameter of 3.6 mm was ensured over a continuous dotting numberof 500, rated 2 when ensured at a dotting number of 100 to 500, andrated 1 when ensured at a dotting number of less than 100.

The presence or absence of hexavalent chromium and trivalent chromium isshown in the item of “chromium class” of Tables 22 and 23. The class was“3” when the entire coated steel sheet was free from trivalent chromiumand hexavalent chromium, “2” when hexavalent chromium was not containedand trivalent chromium was contained, and “1” when hexavalent chromiumwas contained. TABLE 13 Precursor of Polyester Polyol Having at Least 3Functional Groups No. Dicarboxylic Acid Glycol Polyol 701 maleic acidpropylene glycol trimethylolpropane 702 maleic acid propylene glycolglycerin 703 maleic acid 1,6-hexanediol glycerin 704 isophthalic acidpropylene glycol trimethylolpropane 705 isophthalic acid 1,6-hexanediolglycerin a maleic acid 1,6-hexanediol none

TABLE 14 Precursor of Blocked Product of Prepolymer Having NCO Group atthe End, Obtained by Reaction of Organic Polyisocyanate or BlockedProduct Thereof with Active Hydrogen Compound No. Compound Having NCOGroup Blocking Agent 706 tetramethylene diisocyanate phenol 707tetramethylene diisocyanate isopropyl alcohol 708 m-xylene diisocyanateisopropyl alcohol

TABLE 15 Epoxy Resin Having at Least One Secondary Hydroxyl Group orAdduct Thereof No. Epoxy Resin Addition Agent 709 epoxy resin of formula2 shown belows ε-caprolactone where n is 3 on average 710 epoxy resin offormula 2 shown below ε-caprolactone where n is 8 on average 711 epoxyresin of formula 2 shown below ethylene oxide where n is 8 on average

TABLE 16 Composition of Organic Resin Constitutional Ratio (equivalentratio) (a) (b) (c) OH Group equivalent of (a)/regenerated NCO groupPrecursor Precursor Resin of equivalent of (b), or OH group equivalentof Mass ratio No. of Table 2 of Table 3 Table 4 (a) + (c)/ regeneratedNCO group equivalent of (b) of (a):(c) Remarks 712 No. 701 No. 706 none1/1 — Invention 713 No. 701 No. 707 none 1/1 — 714 No. 701 No. 708 none1/1 — 715 No. 702 No. 706 none 1.2/1   — 716 No. 703 No. 707 none1.2/1   — 717 No. 704 No. 708 none 0.8/1   — 718 No. 705 No. 707 none0.9/1   — 719 No. 701 No. 706 No. 709 1/1 7:3 720 No. 701 No. 707 No.710 1/1 7:3 721 No. 705 No. 706 No. 710 1/1 6:4 722 No. 705 No. 707 No.709 1/1 6:4 723 No. 705 No. 707 No. 711 1/1 6:4 724 No. 705 No. 708 No.709 1/1 6:4 A No. a No. 707 No. 709 1/1 6:4 Comparison B No. a No. 708No. 709 1/1 6:4

TABLE 17 Electrically Conducting Particle No. Kind 730 aluminum 731 zinc732 tin 733 common steel 734 stainless steel 735 iron phosphide (Fe₂P₅)736 ferrosilicon (Fe: 55%, Si: 45%) 737 ferrosilicon (Fe: 20%, Si: 80%)738 silicon

TABLE 18 Rust Inhibitor No. Kind 725 a 1/1 (by mass) mixture ofmagnesium secondary phosphate and baked Mn₂O₃.V₂O₅ 726 a 1/1 (by mol)mixture of Ca₃(PO₄)₂ and V₂O₅ 727 strontium chromate 728 magnesiumsecondary phosphate 729 baked 2CaO.V₂O₅

TABLE 19 Undercoating Treatment Undercoating Chemicals (component ratioby Hexavalent Trivalent No. mass) Treating Method Chromium Chromium 739aqueous solution of drying at a sheet + + hexavalent chromic temperatureof 60° C. acid after coating 740 aqueous solution of drying at asheet + + hexavalent chromic temperature of 60° C. acid (50 parts) +fine after coating particulate silica (50 parts) 741 aqueous solution ofdrying at a sheet − + 50% reduced chromic temperature of 60° C. acid(100 parts) + fine after coating particulate silica (30 parts) + etchingfluoride (10 parts) 742 aqueous solution of electro deposition − +hexavalent chromic of trivalent Cr acid 743 aqueous solution of dryingat a sheet − − trivalent chromic acid temperature of 60° C. aftercoating 744 acrylolefin (100 drying at a sheet − − parts) + silanetemperature of 60° C. coupling agent (10 after coating parts) + silica(30 parts) 745 acrylolefin (100 drying at a sheet − − parts) + silanetemperature of 60° C. coupling agent (10 after coating parts) + etchingfloride (10 parts) 746 acrylolefin (100 drying at a sheet − − parts) +silane temperature of 60° C. coupling agent (10 after coating parts) +silica (30 parts) + etching fluoride (10 parts)+: contained,−: not contained

TABLE 20 Specification (1 of 4) of Examples of the Invention andComparative Examples Composition of Organic Film Electrically Rust-Conducting Preventive Organic Resin Pigment Pigment Thickness *CoatedKind Vol % Kind Vol % Kind Vol % (μm) Surface Example 1 No. 712 65 No.737 35 — 0 10 both Example 2 No. 713 65 No. 737 35 — 0 10 both Example 3No. 714 65 No. 737 35 — 0 10 both Example 4 No. 715 65 No. 737 35 — 0 10both Example 5 No. 716 65 No. 737 35 — 0 10 both Example 6 No. 717 65No. 737 35 — 0 10 both Example 7 No. 718 65 No. 737 35 — 0 10 bothExample 8 No. 719 65 No. 737 35 — 0 10 both Example 9 No. 720 65 No. 73735 — 0 10 both Example 10 No. 721 65 No. 737 35 — 0 10 both Example 11No. 722 65 No. 737 35 — 0 10 both Example 12 No. 723 65 No. 737 35 — 010 both Example 13 No. 724 65 No. 737 35 — 0 10 both Example 14 No. 71285 No. 737 15 — 0 10 both Example 15 No. 712 65 No. 737 35 — 0 10 bothExample 16 No. 719 85 No. 737 15 — 0 10 both Example 17 No. 722 65 No.737 35 — 0 10 both Example 18 No. 723 65 No. 730 35 — 0 10 both Example19 No. 719 65 No. 731 35 — 0 10 both Example 20 No. 719 65 No. 732 35 —0 10 both Example 21 No. 719 65 No. 733 35 — 0 10 both Example 22 No.719 65 No. 734 35 — 0 10 both Example 23 No. 719 65 No. 735 35 — 0 10both Example 24 No. 719 65 No. 736 35 — 0 10 both Example 25 No. 719 65No. 738 35 — 0 10 both Example 26 No. 719 60 No. 730 35 No. 725 5 10both Example 27 No. 719 60 No. 731 35 No. 725 5 10 both Example 28 No.719 60 No. 732 35 No. 725 5 10 both Example 29 No. 719 60 No. 733 35 No.725 5 10 both Example 30 No. 719 60 No. 734 35 No. 725 5 10 both Example31 No. 719 60 No. 735 35 No. 725 5 10 both Example 32 No. 719 60 No. 73635 No. 725 5 10 both Example 33 No. 719 60 No. 735 35 No. 726 5 10 bothExample 34 No. 719 60 No. 735 35 No. 727 5 10 both Example 35 No. 719 60No. 736 35 No. 728 5 10 both Example 36 No. 719 60 No. 736 35 No. 729 510 both Example 37 No. 719 65 No. 737 35 — 0 10 both Example 38 No. 71965 No. 737 35 — 0 10 both Example 39 No. 719 65 No. 737 35 — 0 10 bothExample 40 No. 719 65 No. 737 35 — 0 10 both*both: both surfaces

TABLE 21 Specification (2 of 4) of Examples of the Invention andComparative Examples Composition of Organic Film Electrically Rust-Conducting Preventive Organic Resin Pigment Pigment Thickness *CoatedKind Vol % Kind Vol % Kind Vol % (μm) Surface Example 41 No. 719 65 No.737 35 — 0 10 both Example 42 No. 719 65 No. 737 35 — 0 10 both Example43 No. 719 65 No. 737 35 — 0 10 both Example 44 No. 719 40 No. 737 55No. 725 5 10 both Example 45 No. 719 65 No. 737 35 — 0 5 both Example 46No. 719 65 No. 737 35 — 0 7 both Example 47 No. 719 65 No. 737 35 — 0 15both Example 48 No. 719 65 No. 737 35 — 0 10 both Example 49 No. 719 65No. 737 35 — 0 10 both Example 50 No. 719 65 No. 737 35 — 0 10 bothExample 51 No. 719 65 No. 737 35 — 0 10 both Example 52 No. 719 65 No.737 35 — 0 10 both Example 53 No. 719 65 No. 737 35 — 0 10 bothComparative nylon 65 No. 737 35 — 0 10 both Example 1 Comparative epoxy65 No. 737 35 — 0 10 both Example 2 Comparative melamine 65 No. 737 35 —0 10 both Example 3 alkyd Comparative polyester 30 No. 737 70 — 0 10both Example 4 Comparative acryl 90 No. 737 10 — 0 10 both Example 5Comparative No. 719 100 — 0 — 0 10 both Example 6 Comparative No. 720100 — 0 — 0 3 both Example 7 Comparative No. 721 100 — 0 — 0 20 bothExample 8 Comparative No. A 65 No. 737 0 — 0 10 both Example 9Comparative No. B 65 No. 737 35 — 0 10 both Example 10 Comparative No. A65 No. 737 35 — 0 10 both Example 11 Comparative No. A 65 No. 737 35 — 010 both Example 12*both: both surfaces

TABLE 22 Specification (3 of 4) of Examples of the Invention andComparative Examples Plated Layer Cov- Undercoating er- Layer age Cover-Chromi- (g/ age um Kind m²) Kind (mg/m²) Class Example 1 Zn—Nielectroplating 40 No. 745 50 3 Example 2 Zn—Ni electroplating 40 No. 74550 3 Example 3 Zn—Ni electroplating 40 No. 745 50 3 Example 4 Zn—Nielectroplating 40 No. 745 50 3 Example 5 Zn—Ni electroplating 40 No. 74550 3 Example 6 Zn—Ni electroplating 40 No. 745 50 3 Example 7 Zn—Nielectroplating 40 No. 745 50 3 Example 8 Zn—Ni electroplating 40 No. 74550 3 Example 9 Zn—Ni electroplating 40 No. 745 50 3 Example 10 Zn—Nielectroplating 40 No. 745 50 3 Example 11 Zn—Ni electroplating 40 No.745 50 3 Example 12 Zn—Ni electroplating 40 No. 745 50 3 Example 13Zn—Ni electroplating 40 No. 745 50 3 Example 14 Zn—Ni electroplating 40No. 745 50 3 Example 15 Zn—Ni electroplating 40 No. 745 50 3 Example 16Zn—Ni electroplating 40 No. 745 50 3 Example 17 Zn—Ni electroplating 40No. 745 50 3 Example 18 Zn—Ni electroplating 40 No. 745 50 3 Example 19Zn—Ni electroplating 40 No. 745 50 3 Example 20 Zn—Ni electroplating 40No. 745 50 3 Example 21 Zn—Ni electroplating 40 No. 745 50 3 Example 22Zn—Ni electroplating 40 No. 745 50 3 Example 23 Zn—Ni electroplating 40No. 745 50 3 Example 24 Zn—Ni electroplating 40 No. 745 50 3 Example 25Zn—Ni electroplating 40 No. 745 50 3 Example 26 Zn—Ni electroplating 40No. 745 50 3 Example 27 Zn—Ni electroplating 40 No. 745 50 3 Example 28Zn—Ni electroplating 40 No. 745 50 3 Example 29 Zn—Ni electroplating 40No. 745 50 3 Example 30 Zn—Ni electroplating 40 No. 745 50 3 Example 31Zn—Ni electroplating 40 No. 745 50 3 Example 32 Zn—Ni electroplating 40No. 745 50 3 Example 33 Zn—Ni electroplating 40 No. 745 50 3 Example 34Zn—Ni electroplating 40 No. 745 50 3 Example 35 Zn—Ni electroplating 40No. 745 50 3 Example 36 Zn—Ni electroplating 40 No. 745 50 3 Example 37Zn—Ni electroplating 40 No. 739 50 1 Example 38 Zn—Ni electroplating 40No. 740 50 1 Example 39 Zn—Ni electroplating 40 No. 741 50 2 Example 40Zn—Ni electroplating 40 No. 742 50 2

TABLE 23 Specification (4 of 4) of Examples of the Invention andComparative Examples Plated Layer Cov- Undercoating er- Layer age Cover-Chromi- (g/ age um Kind m²) Kind (mg/m²) Class Example 41 Zn—Nielectroplating 40 No. 743 50 2 Example 42 Zn—Ni electroplating 40 No.744 50 3 Example 43 Zn—Ni electroplating 40 No. 746 50 3 Example 44Zn—Ni electroplating 40 No. 745 50 3 Example 45 Zn—Ni electroplating 40No. 745 50 3 Example 46 Zn—Ni electroplating 40 No. 745 50 3 Example 47Zn—Ni electroplating 40 No. 745 50 3 Example 48 Zn—Ni electroplating 40No. 745 50 3 Example 49 Zn—Ni electroplating 40 No. 745 50 3 Example 50Zn—Ni electroplating 20 No. 745 50 3 Example 51 Zn—Ni electroplating 30No. 745 50 3 Example 52 hot-dip 60 No. 745 50 3 galvanization Example 53alloyed hot-dip 50 No. 745 50 3 galvanization Comparative Zn—Nielectroplating 40 No. 745 50 3 Example 1 Comparative Zn—Nielectroplating 40 No. 745 50 3 Example 2 Comparative Zn—Nielectroplating 40 No. 745 50 3 Example 3 Comparative Zn—Nielectroplating 40 No. 745 50 3 Example 4 Comparative Zn—Nielectroplating 40 No. 745 50 3 Example 5 Comparative Zn—Nielectroplating 40 No. 745 50 3 Example 6 Comparative Zn—Nielectroplating 40 No. 745 50 3 Example 7 Comparative Zn—Nielectroplating 40 No. 745 50 3 Example 8 Comparative Zn—Nielectroplating 40 No. 745 5 3 Example 9 Comparative Zn—Ni electroplating40 No. 745 150 3 Example 10 Comparative Zn electroplating 5 No. 745 50 3Example 11 Comparative hot-dip 120 No. 745 50 3 Example 12 galvanization

TABLE 24 Evaluation Results (1 of 2) of Examples of the Invention andComparative Examples Corrosion Resistance Formability after Cup DrawingWeldability Example 1 3 4 3 Example 2 3 4 3 Example 3 3 4 3 Example 4 34 3 Example 5 3 4 3 Example 6 3 4 3 Example 7 3 4 3 Example 8 4 4 3Example 9 4 4 3 Example 10 4 4 3 Example 11 4 4 3 Example 12 4 4 3Example 13 4 4 3 Example 14 4 4 3 Example 15 3 4 3 Example 16 4 4 3Example 17 4 4 3 Example 18 4 3 3 Example 19 4 3 3 Example 20 4 3 3Example 21 4 3 3 Example 22 4 3 3 Example 23 4 3 3 Example 24 4 3 3Example 25 4 4 3 Example 26 4 4 3 Example 27 4 4 3 Example 28 4 4 3Example 29 4 4 3 Example 30 4 4 3 Example 31 4 4 3 Example 32 4 4 3Example 33 4 4 3 Example 34 4 4 3 Example 35 4 4 3 Example 36 4 4 3Example 37 3 4 3 Example 38 3 4 3 Example 39 3 4 3 Example 40 3 4 3

TABLE 25 Evaluation Results (2 of 2) of Examples of the Invention andComparative Examples Outer Surface Inner Surface Corrosion CorrosionResistance Resistance Formability Example 41 3 4 3 Example 42 3 4 3Example 43 3 4 3 Example 44 2 3 3 Example 45 4 2 3 Example 46 4 3 3Example 47 3 4 2 Example 48 4 4 3 Example 49 4 4 2 Example 50 4 4 3Example 51 4 4 3 Example 52 4 4 2 Example 53 4 4 3 Comparative 1 nottested not tested Example 1 Comparative 1 not tested not tested Example2 Comparative 1 not tested not tested Example 3 Comparative 1 not testednot tested Example 4 Comparative 1 not tested not tested Example 5Comparative 4 not tested 1 Example 6 Comparative 4 not tested 1 Example7 Comparative 4 not tested 1 Example 8 Comparative 1 not tested nottested Example 9 Comparative 1 not tested not tested Example 10Comparative 1 not tested not tested Example 11 Comparative 1 not testednot tested Example 12

Evaluation results are as shown in Tables 24 and 25. In Examples 1 to 53of the present invention, the score is 2 or higher in all of theformability test, test on corrosion resistance after cup drawing andweldability test. Depending on the constitution of Examples, a higherperformance, having a score of 3, is exhibited.

In the case of intending not to contain trivalent chromium andhexavalent chromium, Examples in the “chromium class 3” come under thecase, and in the case of intending not to contain hexavalent chromium,Examples in the “chromium class 2” come under the case.

Comparative Examples 1 to 12 in Tables 24 and 25 show cases of using acoated steel sheet out of the scope of the present invention.

In Comparative Examples 1, 2 and 3 where the resins are differing in thekind, the formability is bad.

In Comparative Example 4 where the resin content in the film is small,the formability is bad.

In Comparative Examples 5 and 6 where the content of the electricallyconducting particle in the film is small, the weldability is bad.

In Comparative Example 7 where the film coverage is too small, thecorrosion resistance is bad.

In Comparative Example 8 where the film coverage is too large, theweldability is bad and the formability is slightly worsened.

In Comparative Example 9 where the undercoating coverage is too small,the corrosion resistance is bad.

In Comparative Example 10 where the undercoating coverage is too large,the weldability is bad.

In Comparative Example 11 where the plating coverage is too small, thecorrosion resistance is bad.

In Comparative Example 12 where the plating coverage is too large, theweldability is bad.

Example 8

The conditions when an electrically conducting particle orrust-preventive pigment of various types was mixed in a resin systemcontaining a urethane bond are shown in Table 26. The following fiveresins were used as the resin containing a urethane bond.

-   -   Resin A: A resin system produced by mixing a polyol comprising        maleic acid, propylene glycol and trimethylolpropane, and a        tetramethylene diisocyanate blocked with phenol at an equivalent        ratio of OH group equivalent/regenerated NCO group        equivalent=1/1.    -   Resin B: A resin system produced by mixing a polyol comprising        maleic acid, propylene glycol and trimethylpropanolamine, a        tetramethylene diisocyanate blocked with phenol, and an epoxy        resin using ε-caprolactone as the addition agent and having        formula 2 where n is 3 on average, at an equivalent ratio of OH        group equivalent/regenerated NCO group equivalent=1/1; the mass        ratio between polyol and epoxy resin is 7:3.    -   Resin C: A resin system produced by mixing a polyol comprising        isophthalic acid, 1,6-hexanediol and glycerin, an m-xylene        diisocyanate blocked with isopropyl alcohol, and an epoxy resin        using ε-caprolactone as the addition agent and having formula 2        where n is 3 on average, at an equivalent ratio of OH group        equivalent/regenerated NCO group equivalent=1.2/1; the mass        ratio between polyol and epoxy resin is 6:4.    -   Resin D: Bisphenol-type epoxy resin (commercially available        product)    -   Resin E: Acryl resin (commercially available product)

An electrically conducting particle having a predetermined particle sizedistribution and/or a predetermined rust inhibitor wereblended•dispersed at the blending ratio shown in Table 26 in the resinprepared above and the obtained coating material was applied to a platedsteel sheet subjected to an undercoating treatment, and then baked•driedat a peak steel temperature of 220° C., whereby coated metal sheets wereproduced. These coated metal sheets were evaluated on the weldability,formability and corrosion resistance under the same conditions as inExample 1. TABLE 26 Specification of Coated Metal Sheet ElectricallyConducting Particles Mode Value for Number Base Sheet for DistributionMode value Coating Mode for volume Maximum Rust-Preventive *²Under-Resin, Value, Number of Distribution Particle Pigment Film No. *¹Kindcoating Kind *³Kind Vol % μm Particles, % μm Size, μm *⁴Kind Vol %Thickness, μm 801 EG Treatment 1 Resin A Particle 1 3 0.50 7 18.2 23.3 —— 9 802 EG Treatment 1 Resin A Particle 1 15 0.50 7 18.2 23.3 — — 9 803EG Treatment 1 Resin A Particle 2 25 2.05 7 45.0 55.2 — — 9 804 EGTreatment 1 Resin A Particle 3 25 0.50 7 18.2 23.3 Pigment 1 5 9 805 EGTreatment 2 Resin A Particle 1 25 0.50 7 18.2 23.3 Pigment 1 10 9 806 EGTreatment 1 Resin A Particle 1 65 0.50 7 18.2 23.3 Pigment 1 20 9 807 ZLTreatment 1 Resin A Particle 1 25 0.50 7 18.2 23.3 Pigment 2 10 9 808 ZLTreatment 1 Resin A Particle 1 25 0.50 7 18.2 23.3 Pigment 3 10 9 809 ZLTreatment 1 Resin B Particle 1 25 0.50 7 18.2 23.3 Pigment 2 10 9 810 ZLTreatment 1 Resin C Particle 1 25 0.50 7 18.2 23.3 Pigment 2 10 9 811 ZLTreatment 1 Resin D Particle 1 25 0.50 7 18.2 23.3 Pigment 2 10 9 812 ZLTreatment 1 Resin E Particle 1 25 0.50 7 18.2 23.3 Pigment 2 10 9*¹EG: zinc electroplated steel sheet (plating coverage: 40 g/m²)ZL: zinc-12% nickel electroplated steel sheet (plating coverage: 40g/m²)*²Treatment 1: trivalent chromium-treated film (film coverage: 50 mg/m²[in terms of chromium])Treatment 2: acrylolefin (100 parts by mass) + silane coupling agent (10parts by mass) + silica (30 parts by mass) + etching fluoride (10 partsby mass)*³Particle 1: 76%-silicon-containing ferrosilicon particleParticle 2: 76%-silicon-containing ferrosilicon particleParticle 3: Particle 1 (95 vol %) + stainless steel particle (5 vol %)The stainless steel particle used here had, by itself, a particle sizedistribution such that the mode value for number distribution was 2.5μm, the number of particles was 10%, and the mode value for volumedistribution was 10 μm.*⁴Pigment 1: magnesium secondary phosphate (50 parts by mass) + bakedMn₂O₃.V₂O₅ (50 parts by mass)Pigment 2: a 1/1 (by mol) mixture of Ca₃(PO₄)₂ and V₂O₅Pigment 3: a 1/1 (by mol) mixture (50 parts by mass) of Ca₃(PO₄)₂ andV₂O₅ + fumed silica (50 parts by mass)

The results are shown in Table 27. By using a resin system having aurethane bond and, at the same time, using an electrically conductingparticle having a particle size distribution within the scope of thepresent invention, weldability, formability and corrosion resistance ingood balance are obtained. In the system using a resin having a urethanebond, the formability is good as compared with the epoxy resin system ofExample 811 and the acryl resin system of Example 812.

Nos. 801, 803 and 806 for comparison are showing cases of using a coatedmetal sheet out of the scope of the present invention. In No. 801 wherethe amount of the electrically conducting particle is too small, theelectric conductivity cannot be obtained. In No. 803 where the modevalue for the number distribution is too large, the formability and thecorrosion resistance are greatly decreased. In No. 806 where the amountof the electrically conducting particle is too large, the formability isgreatly decreased. TABLE 27 Performance Evaluation Results FormabilityCorrosion Resistance Weldability, Electric Cylindrical Cycle NumberCycle Appearance dotting Conductivity, Drawing, Beading, of CylindricalNumber of of End No. number mΩ appearance appearance Drawn Part BeadedPart Face Part Remarks 801 0 —^(note*)) ◯ ◯ 300 250 Δ Comparison 802 8001.1 ⊙ ⊙ 400 350 ◯ Example 803 1200 0.03 Δ Δ 200 100 Δ Comparison 8041800 0.05 ⊙ ⊙ 450 400 ⊙ Example 805 1700 0.03 ⊙ ⊙ 300 250 ◯ Example 8061700 0.04 Δ Δ 250 150 ⊙ Comparison 807 2200 0.03 ⊙ ⊙ 600 500 ◯ Example808 2200 0.05 ⊙ ⊙ 600 500 ◯ Example 809 2000 0.03 ⊙ ⊙ 600 500 ◯ Example810 2100 0.04 ⊙ ⊙ 600 500 ◯ Example 811 1500 0.07 ◯ ◯ 500 400 ◯ Example812 1500 0.15 ◯ ◯ 500 400 ◯ Example^(note))—: not measurable (∞)

Example 9

The steel having components shown in Table 28 was ingotted into a bloomby a normal converter-vacuum degassing treatment and the bloom washot-rolled and then cold-rolled under ordinary conditions to obtain acold-rolled steel sheet (thickness: 0.8 mm). By using this steel sheetas the material, various surface-treated steel sheets were produced. Thehot-dip plating was performed in a line using of a Sendzimir system or aflux system. In the case of Sendzimir system, the annealing wasperformed within the line. The annealing temperature was from 800 to850° C. After the plating, the plating coverage was adjusted by a gaswiping method. At this time, the plating temperature which variesaccording to the plating composition was set to the melting point ofplating composition +40° C. The electroplating was performed in anelectroplating line after annealing the cold-rolled steel sheet. TABLE28 Components of Base Sheet for Plating (mass %) Symbol C Si Mn P S TiAl B N I 0.0012 0.03 0.32 0.007 0.009 0.054 0.04 0.0003 0.0033 II 0.00200.09 0.32 0.008 0.011 0.040 0.04 — 0.0032

On both surfaces of the surface-treated steel sheet obtained above, anundercoating film having the composition shown in Table 35 was coated bya roll coater to a predetermined coverage and baked and dried with hotair at 200° C. Furthermore, an electrically conductingpigment-containing organic film having the composition shown in Tables29 to 34 was coated by a roll coater on both surfaces or one surface (onthe outer side) to a predetermined coverage and then baked and driedwith a hot air at 250° C. In some levels, skin pass rolling was appliedto the surface-treated steel sheet and applied also after the coating ofthe organic film to adjust the roughness and texture of the surface. Thespecifications of the thus-obtained rust-preventive steel sheets areshown in Tables 36 to 39.

The steel sheets produced as above were evaluated on the aptitude as afuel tank by the following method.

(1) Evaluation of Corrosion Resistance

(a) Outer Surface Corrosion Resistance

The steel sheet after coating was formed by cylindrical cup drawing suchthat the coated surface came the outer side, and was then subjected to acycle corrosion test. In the cylindrical cup drawing, the steel sheetwas coated with a rust-preventive oil, left in the erected state for 1hour to 1 hour and 30 minutes and then drawn at a drawing ratio of 2.0with a punch diameter of 50 mm under an unwrinkling pressure of 9.8 kN.

In the cycle corrosion test, one cycle was 8 hours in total consistingof salt water spraying for 2 hours, drying for 4 hours and dampening for2 hours. The salt water spraying was performed under the conditionsaccording to JIS-K5400. The drying conditions were a temperature of 50°C. and a humidity of 30% RH or less, and the dampening conditions were atemperature of 35° C. and a humidity of 95% RH or more.

The corrosion resistance was evaluated according to the following ratingscale.

Score 4+: Red rust indicating the decrease in the thickness of the steelsheet was not generated even after 300 cycles and white rust indicatingthe corrosion of the plating layer was covering the sample in an arearatio of less than 5% of the entire area.

Score 4: Red rust indicating the decrease in the thickness of the steelsheet was not generated even after 300 cycles and white rust indicatingthe corrosion of the plating layer was covering the sample in an arearatio of 5% to less than 50% of the entire area.

Score 3: Red rust indicating the decrease in the thickness of the steelsheet was not generated even after 300 cycles.

Score 2: Red rust was not observed after 100 cycles but observed after300 cycles.

Score 1: Red rust was observed after 100 cycles.

(b) Inner Surface Corrosion Resistance

The corrosion resistance against gasoline was evaluated. As for themethod therefor, a test solution was poured in a sample deep-drawn intoa flat-bottom cylinder having a flange width of 20 mm, a diameter of 50mm and a depth of 25 mm by a hydraulic forming tester, and a glass coverwas secured thereon through a silicon rubber-made ring. After this test,the corroded state was observed by eye.

(Test Conditions)

Test solution:gasoline+distilled water (10%)+formic acid (200 ppm)Test period: left standing at 40° C. for 3 months.(Criteria of Evaluation)

Score 4: No change.

Score 3: White rust generation ratio was 1% or less.

Score 2: Red rust generation ratio was 5% or less or white rustgeneration ratio was from 1 to 50%.

Score 1: Red rust generation ratio was exceeding 5% or conspicuous whiterust.

(2) Evaluation of Press Workability

A forming test at a drawing ratio of 2.3 was performed by using ahydraulic forming tester and a cylindrical punch having a diameter of 50mm. At this time, the unwrinkling pressure was 4.9 kN. The formabilitywas evaluated according to the following criteria.

Score 4: Formable and no defect in the plating layer. The film state wascompletely normal without a lack of luster or the like in the formedpart.

Score 3: Formable but a flaw was slightly generated in the platinglayer. The film formed part was changed in the color tone but free fromcracking or separation.

Score 2: Formable but a large flaw was generated in the plating layerand film cracking was observed.

Score 1: Not formable.

(3) Evaluation of Weldability

The weldability was evaluated by the spot welding continuous dottingproperty and seam weldability.

(a) Spot Welding

Spot welding was performed by using a R40 chromium-copper electrodehaving a tip diameter of 6 mm at a welding current of 10 kA under anapplied pressure of 1.96 kN for a welding time of 12 cycles, and thecontinuous dotting number before the nugget diameter decreased below4{square root}{square root over (t)} (where t=sheet thickness) wasevaluated.

Score 4: Continuous dotting number of 500 or more.

Score 3: Continuos dotting number of 300 to less than 500.

Score 2: Continuous dotting number of 100 to less than 300.

Score 1: Continuous dotting number of less than 100.

(b) Seam Weldability

Seam welding of 10 m was performed with 2-on/1-off electrification at awelding current of 11 kA and an applied pressure of 4.9 kN by using anelectrode ring having a tip R of 6 mm and a diameter of 250 mm.Thereafter, a specimen according to JIS-Z-3141 was prepared and testedon the leakage.

Score 4: No leakage.

Score 3: No leakage but the welded part surface was slightly roughened.

Score 2: No leakage but defects such as cracking were generated on thewelded part surface.

Score 1: Leakage was generated. TABLE 29 Precursor of Polyester PolyolHaving at Least 3 Functional Groups No. Dicarboxylic Acid Glycol Polyol901 maleic acid propylene glycol trimethylolpropane 902 maleic acidpropylene glycol glycerin 903 maleic acid 1,6-hexanediol glycerin 904isophthalic acid propylene glycol trimethylolpropane 905 isophthalicacid 1,6-hexanediol glycerin

TABLE 30 Precursor of Blocked Product of Prepolymer Having NCO Group atthe End, Obtained by Reaction of Organic Polyisocyanate or BlockedProduct Thereof with Active Hydrogen Compound No. Compound Having NCOGroup Blocking Agent 906 tetramethylene diisocyanate phenol 907tetramethylene diisocyanate isopropyl alcohol 908 n-xylene diisocyanateisopropyl alcohol

TABLE 31 Epoxy Resin Having at Least One Secondary Hydroxyl Group orAdduct Thereof No. Epoxy Resin Addition Agent 909 epoxy resin of formula(1) where n is ε-caprolactone 3 on average 910 epoxy resin of formula(1) where n is ε-caprolactone 8 on average 911 epoxy resin of formula(1) where n is ethylene oxide 8 on average

TABLE 32 Composition of Organic Resin Constitutional Ratio (equivalentratio) OH Group equivalent of (a)/regenerated NCO group equivalent of(b), or OH group equivalent of (a) + (c)/ Mass (a) (b) (c) regeneratedNCO ratio Precursor Precursor Resin of group equivalent of No. of Table2 of Table 3 Table 4 of (b) (a):(c) Remarks 912 No. 901 No. 906 none 1/1— Invention 913 No. 901 No. 907 none 1/1 — 914 No. 901 No. 908 none 1/1— 915 No. 902 No. 906 none 1.2/1   — 916 No. 903 No. 907 none 1.2/1   —917 No. 904 No. 908 none 0.8/1   — 918 No. 905 No. 907 none 0.9/1   —919 No. 901 No. 906 No. 909 1/1 7:3 920 No. 901 No. 907 No. 910 1/1 7:3921 No. 905 No. 906 No. 910 1/1 6:4 922 No. 905 No. 907 No. 909 1/1 6:4923 No. 905 No. 907 No. 911 1/1 6:4 924 No. 905 No. 908 No. 909 1/1 6:4

TABLE 33 Electrically Conducting Pigment No. Kind 925 aluminum 926 zinc927 nickel 928 stainless steel 929 iron phosphide (Fe₂P₅) 930ferrosilicon (Fe: 55%, Si: 45%) 931 ferrosilicon (Fe: 20%, Si: 80%) 932a 10/1 (by mol) mixture of ferrosilicon (Fe: 20%, Si: 80%) and stainlesssteel 933 silicon

TABLE 34 Rust-Preventive Pigment No. Kind 934 a mixture of magnesiumsecondary phosphate (50 parts by mass) and baked Mn₂O₃.V₂O₅ (50 parts bymass) 935 a 1/1 (by mol) mixture of Ca₃(PO₄)₂ and V₂O₅ 936 strontiumchromate 937 magnesium secondary phosphate 938 baked 2CaO.V₂O₅

TABLE 35 Undercoating Treatment Undercoating Chemicals HexavalentTrivalent No. (component ratio by mass) Chromium Chromium 939 aqueoussolution of hexavalent chromic acid:fine particulate silica = 50:50 + +940 aqueous solution of hexavalent chromic acid:fine particulatesilica:etching fluoride = 100:30:10 + + 941 aqueous solution ofhexavalent chromic + + acid 942 aqueous solution of trivalent chromicacid − + 943 phenol resin:silane coupling agent:phosphoric acid =100:10:10 − − 944 phenol resin:silane coupling agent:phosphoricacid:silica = 100:10:10:20 − − 945 acrylolefin:silane couplingagent:silica = 100:10:30 − − 946 acrylolefin:silane couplingagent:silica:tannic acid = 100:10:30:10 − −+: contained,−: not contained

TABLE 36 Specification (1 of 4) of Coated Metal Sheet Plating LayerUndercoating Layer Coverage Coverage Steel Sheet Kind (g/m²) Kind(mg/m²) Example 1 I Zn electroplating 40 No. 942 50 Example 2 II Znelectroplating 40 No. 942 50 Example 3 I Zn electroplating 40 No. 942 50Example 4 I Zn—12% Ni electroplating 40 — — Example 5 I Zn—12% Nielectroplating 40 No. 942 50 Example 6 I Zn—12% Ni electroplating 20 No.942 50 Example 7 I Zn—12% Ni electroplating 50 No. 942 50 Example 8 IZn—12% Ni electroplating 40 No. 942 50 Example 9 I Zn—12% Nielectroplating 40 No. 942 50 Example 10 I Zn—12% Ni electroplating 40No. 942 50 Example 11 I Zn—12% Ni electroplating 40 No. 942 50 Example12 I Zn—12% Ni electroplating 40 No. 942 50 Example 13 I Zn—12% Nielectroplating 40 No. 942 50 Example 14 I Zn—12% Ni electroplating 40No. 942 50 Example 15 I Zn—12% Ni electroplating 40 No. 942 50 Example16 I Zn—12% Ni electroplating 40 No. 942 50 Example 17 I Zn—12% Nielectroplating 40 No. 942 50 Example 18 I hot-dip Zn plating 50 No. 94250 Example 19 I hot-dip Zn plating 50 No. 942 50 Example 20 I hot-dip Znplating 50 No. 942 50 Example 21 I hot-dip Zn plating 50 No. 942 50Example 22 I hot-dip Zn plating 50 No. 942 50 Example 23 I hot-dip Znplating 50 No. 942 50 Example 24 I hot-dip Zn plating 50 No. 942 50Example 25 I hot-dip Zn plating 50 No. 942 50 Example 26 I alloyedhot-dip Zn 45 No. 942 50 plating Example 27 I alloyed hot-dip Zn 45 No.942 50 plating Example 28 I alloyed hot-dip Zn 45 No. 942 50 platingExample 29 I alloyed hot-dip Zn 45 No. 942 50 plating

TABLE 37 Specification (2 of 4) of Coated Metal Sheet Plating LayerUndercoating Layer Coverage Coverage Steel Sheet Kind (g/m²) Kind(mg/m²) Example 30 I hot-dip Al—9% Si plating 40 No. 939 20 Example 31 Ihot-dip Al—9% Si plating 40 No. 940 20 Example 32 I hot-dip Al—9% Siplating 40 No. 941 20 Example 33 I hot-dip Al—9% Si plating 40 No. 94250 Example 34 I hot-dip Al—9% Si plating 40 No. 944 300 Example 35 Ihot-dip Al—9% Si plating 40 No. 945 100 Example 36 I hot-dip Al—9% Siplating 40 No. 946 100 Example 37 I hot-dip Sn—8% Zn plating 40 — —Example 38 I hot-dip Sn—8% Zn plating 40 — — Example 39 I hot-dip Sn—8%Zn plating 40 — — Example 40 I hot-dip Sn—8% Zn plating 40 No. 943 300Example 41 I hot-dip Sn—8% Zn plating 40 No. 943 300 Example 42 Ihot-dip Sn—8% Zn plating 40 No. 943 300 Example 43 I hot-dip Sn—8% Znplating 20 No. 943 300 Example 44 I hot-dip Sn—8% Zn plating 30 No. 943300 Example 45 I hot-dip Sn—8% Zn plating 60 No. 943 300 Example 46 Ihot-dip Sn—8% Zn plating 50 No. 943 300 Comparative I hot-dip Zn plating50 No. 942 50 Example 1 Comparative I Zn—12% Ni electroplating 40 No.942 50 Example 2 Comparative I Zn—12% Ni electroplating 40 No. 942 50Example 3 Comparative I Zn—12% Ni electroplating 40 No. 942 50 Example 4Comparative I Zn—12% Ni electroplating 40 No. 942 50 Example 5Comparative I Zn—12% Ni electroplating 40 No. 942 50 Example 6Comparative I Zn—12% Ni electroplating 40 No. 942 50 Example 7Comparative I hot-dip Al—9% Si plating 40 No. 942 50 Example 8Comparative I hot-dip Al—9% Si plating 40 No. 942 50 Example 9Comparative I hot-dip Al—9% Si plating 40 No. 942 50 Example 10Comparative I hot-dip Al—9% Si plating 40 No. 942 50 Example 11Comparative I hot-dip Al—9% Si plating 40 — — Example 12

TABLE 38 Specification (3 of 4) of Coated Metal Sheet Composition ofOrganic Film Electrically Rust- Organic Conducting Preventive ResinPigment Pigment Thickness *Coated Kind Vol % Kind Vol % Kind Vol % (μm)Surface Example 1 No. 912 65 No. 932 35 — 0 12 both Example 2 No. 912 65No. 932 35 — 0 12 both Example 3 No. 912 65 No. 932 35 — 0 12 bothExample 4 No. 912 65 No. 932 35 — 0 12 both Example 5 No. 912 65 No. 93235 — 0 12 both Example 6 No. 913 60 No. 932 35 No. 934 5 12 both Example7 No. 914 60 No. 932 35 No. 934 5 12 both Example 8 No. 915 60 No. 93235 No. 934 5 12 both Example 9 No. 916 60 No. 932 35 No. 934 5 12 bothExample 10 No. 917 60 No. 932 35 No. 934 5 12 both Example 11 No. 918 60No. 932 35 No. 934 5 12 both Example 12 No. 919 60 No. 932 35 No. 934 512 both Example 13 No. 920 60 No. 932 35 No. 934 5 12 both Example 14No. 921 80 No. 932 15 No. 934 5 12 both Example 15 No. 922 60 No. 932 45No. 934 5 12 both Example 16 No. 923 80 No. 932 15 No. 934 5 12 bothExample 17 No. 924 50 No. 932 45 No. 934 5 12 both Example 18 No. 919 60No. 932 35 No. 934 5 12 both Example 19 No. 919 60 No. 932 35 No. 934 512 both Example 20 No. 919 60 No. 925 35 No. 934 5 12 both Example 21No. 919 60 No. 926 35 No. 934 5 12 both Example 22 No. 919 60 No. 927 35No. 934 5 12 both Example 23 No. 919 60 No. 928 35 No. 934 5 12 bothExample 24 No. 919 60 No. 929 35 No. 934 5 12 both Example 25 No. 919 60No. 930 35 No. 934 5 12 both Example 26 No. 919 60 No. 931 35 No. 935 512 both Example 27 No. 919 60 No. 933 35 No. 936 5 12 both Example 28No. 919 60 No. 932 35 No. 937 5 12 both Example 29 No. 919 60 No. 932 35No. 938 5 12 both*both: both surfaces

TABLE 39 Specification (4 of 4) of Coated Metal Sheet Composition ofOrganic Film Electrically Rust- Organic Conducting Preventive ResinPigment Pigment Thickness *Coated Kind Vol % Kind Vol % Kind Vol % (μm)Surface Example 30 No. 919 60 No. 932 35 No. 934 5 10 both Example 31No. 919 60 No. 932 35 No. 934 5 10 both Example 32 No. 919 60 No. 932 35No. 934 5 10 both Example 33 No. 919 60 No. 932 35 No. 934 5 10 bothExample 34 No. 919 60 No. 932 35 No. 934 5 10 both Example 35 No. 919 65No. 932 35 — 0 10 both Example 36 No. 919 65 No. 932 35 — 0 10 bothExample 37 No. 919 40 No. 932 35 No. 934 5 5 both Example 38 No. 919 60No. 932 35 No. 934 5 15 both Example 39 No. 919 60 No. 932 35 No. 934 525 both Example 40 No. 919 60 No. 932 35 No. 934 5 10 one Example 41 No.919 60 No. 932 35 No. 934 5 10 one Example 42 No. 919 60 No. 932 35 No.934 5 10 one Example 43 No. 919 60 No. 932 35 No. 934 5 10 one Example44 No. 919 60 No. 932 35 No. 934 5 10 one Example 45 No. 919 60 No. 93235 No. 934 5 10 one Example 46 No. 919 60 No. 932 35 No. 934 5 10 oneComparative No. 919 25 No. 932 70 No. 934 5 1 both Example 1 ComparativeNo. 919 25 No. 932 55 No. 934 20 10 both Example 2 Comparative No. 91965 No. 932 35 — 0 35 both Example 3 Comparative No. 919 65 No. 932 35 —0 12 both Example 4 Comparative No. 919 65 No. 932 35 — 0 10 bothExample 5 Comparative No. 919 65 No. 932 35 — 0 10 both Example 6Comparative No. 919 100 — 0 — 0 10 both Example 7 Comparative epoxy 95 —0 No. 934 5 10 both Example 8 Comparative Poly- 95 — 0 No. 934 5 10 bothExample 9 ester Comparative acryl- 65 No. 932 35 — 0 10 both Example 10Comparative acryl- 65 No. 932 35 — 0 10 both Example 11 epoxyComparative acryl- 65 No. 932 35 — 0 10 both Example 12 urethane*one: only outer surface side, both: both surfaces

TABLE 40 Performance Evaluation Results (1 of 2) Surface Surface TextureOuter Inner Roughness Pc Surface Surface Ra Rmax (peaks/ CorrosionCorrosion Spot Seam (μm) (μm) 10 mm) Resistance Resistance FormabilityWeldability Weldability Example 1 0.72 9.16 74 3 3 4 4 4 Example 2 0.7212.48 66 4 3 4 4 4 Example 3 1.48 13.40 154 4 3 4 3 3 Example 4 1.4814.04 141 3 3 4 4 4 Example 5 0.92 6.20 79 4 3 4 4 4 Example 6 0.45 5.2365 3 3 3 4 4 Example 7 0.68 7.72 105 4 3 4 4 4 Example 8 0.40 5.55 117 33 3 4 4 Example 9 0.56 6.87 100 4 3 4 4 4 Example 10 0.65 6.05 98 4 3 44 4 Example 11 0.88 6.03 65 4 3 4 4 4 Example 12 0.90 7.06 68 4 3 4 3 3Example 13 0.84 8.01 102 4 3 4 4 4 Example 14 0.88 8.98 78 4 3 4 3 3Example 15 0.79 8.05 68 4 3 4 4 4 Example 16 0.88 7.65 64 4 3 4 4 4Example 17 0.80 7.88 85 4 3 4 4 4 Example 18 1.10 12.20 125 4 3 4 4 4Example 19 1.12 15.88 185 4 3 4 3 3 Example 20 1.35 16.00 165 4 3 4 3 3Example 21 1.55 16.50 178 4 3 4 3 3 Example 22 1.02 13.10 125 4 3 4 4 4Example 23 1.32 15.08 141 4 3 4 4 4 Example 24 0.98 7.05 70 4 3 4 4 4Example 25 1.01 7.98 65   4+ 3 4 4 4 Example 26 0.78 10.12 120   4+ 3 44 4 Example 27 0.77 9.32 105   4+ 3 4 4 4 Example 28 0.65 7.54 89 4 3 44 4 Example 29 0.66 6.98 68 4 3 4 4 4

TABLE 41 Performance Evaluation Results (2 of 2) Surface Surface TextureOuter Inner Roughness Pc Surface Surface Ra Rmax (peaks/ CorrosionCorrosion Spot Seam (μm) (μm) 10 mm) Resistance Resistance FormabilityWeldability Weldability Example 30 0.95 7.35 65 4 4 4 4 4 Example 310.93 7.68 87 4 4 4 4 4 Example 32 1.05 7.98 98 4 4 4 4 4 Example 33 0.688.64 85 4 4 4 4 4 Example 34 0.78 6.90 75 4 4 4 4 4 Example 35 0.79 8.2571 4 4 4 4 4 Example 36 0.78 6.56 68 4 4 4 4 4 Example 37 1.68 7.31 98 33 3 4 4 Example 38 0.70 7.92 63 4 4 4 3 4 Example 39 0.66 5.86 68 4 4 43 3 Example 40 0.85 6.89 100   4+ 4 4 4 4 Example 41 0.86 8.01 85   4+ 44 4 4 Example 42 0.85 7.45 91   4+ 4 4 4 4 Example 43 0.80 6.89 72 4 4 44 4 Example 44 0.82 7.84 65 4 4 4 4 4 Example 45 0.79 6.85 84   4+ 4 4 44 Example 46 0.68 7.48 69   4+ 4 4 4 4 Comparative 1.52 6.57 253 2 1 2 42 Example 1 Comparative 2.85 19.50 198 4 3 4 2 2 Example 2 Comparative0.66 5.54 21 4 3 3 2 1 Example 3 Comparative 2.88 25.50 220 3 3 4 2 2Example 4 Comparative 2.55 19.65 302 2 3 4 3 2 Example 5 Comparative3.15 28.80 190 2 3 4 2 2 Example 6 Comparative 0.78 7.56 65 1 2 4 1 1Example 7 Comparative 0.85 7.88 78 2 2 3 1 1 Example 8 Comparative 0.658.25 96 2 2 3 1 1 Example 9 Comparative 0.87 6.87 66 2 2 2 4 4 Example10 Comparative 0.95 9.40 80 2 2 2 4 4 Example 11 Comparative 0.79 8.3177 2 2 2 4 4 Example 12

Evaluation results are as shown in Tables 40 and 41. In Examples of thepresent invention, the score is 3 or higher in all of the corrosionresistance test, formability test and weldability test. Depending on theconstitution of Examples, a higher performance having a score of 4 isexhibited. Particularly, when the surface roughness of the organic resinfilm is controlled to 0.3 to 2.5 μm as Ra and 20 μm or less as Rmax andthe Pc of the surface texture is controlled to 10 to 200 peaks per 10-mmlength with a count level of 0.3 μm, stable welding formability andcorrosion resistance are exhibited. Also, in the system where theorganic film is formed by using a raw material film-forming resincontaining (a) a polyester polyol having at least three functionalgroups, (b) a blocked organic polyisocyanate or a blocked product of aprepolymer having an NCO group at the end obtained by the reaction of anorganic polyisocyanate with an active hydrogen compound, and (c) anepoxy resin having at least one secondary hydroxyl group or an adductthereof and in the system using ferrosilicon as the electricallyconducting pigment, good outer surface corrosion resistance isexhibited.

Comparative Examples 1 to 12 in Table 41 show cases of using a coatedsteel sheet out of the scope of the present invention. In ComparativeExample 1 where the thickness of the organic film is small, thecorrosion resistance and formability are insufficient. Also, as the Pcis high, the seam weldability is slightly bad. In Comparative Example 2where the Ra value is high, the spot weldability is bad and in the seamwelding, troubles are generated. In Comparative Example 3 where the filmthickness is too large, the weldability is bad. In Comparative Examples4, 5 and 6 where the surface roughness Ra is high and the Rmax and/orsurface texture Pc are high, the spot weldability and seam weldabilityare bad. In Comparative Example 7 where an electrically conductingpigment is not contained in the film, the weldability is bad. InComparative Examples 8, 9, 10, 11, and 12 where the resin film is out ofthe scope of the present invention, the corrosion resistance afterforming is poor. In Comparative Examples 8 and 9 where an electricallyconducting pigment is not contained, the weldability is also bad. InComparative Example 12 where an undercoating film is not formed, theformability is bad and in turn the corrosion resistance is decreased.

Example 10

The steel having components shown in Table 42 was ingotted into a bloomby a normal converter-vacuum degassing treatment and the bloom washot-rolled and then cold-rolled under ordinary conditions to obtain acold-rolled steel sheet (thickness: 0.8 mm). By using this steel sheetas the material, hot-dip tin plating or tin-based alloy plating wasperformed. For the hot-dip plating, a line using a Sendzimir system or aflux system was used. In the case of a Sendzimir system, the annealingwould be performed within the line. The annealing temperature was from800 to 850° C. After the plating, the plating coverage was adjusted by agas wiping method. At this time, the plating temperature which variesaccording to the plating composition was set to the melting point ofplating composition +40° C. On both surfaces of the tin-plated ortin-based alloy-plated steel sheet obtained above, an undercoating filmhaving the composition shown in Table 49 was coated by a roll coater toa predetermined coverage and baked and dried with hot air at 200° C.Furthermore, an electrically conducting pigment-containing organic filmhaving the composition shown in Tables 43 to 48 was coated by a rollcoater on both surfaces or one surface (on the outer side) to apredetermined coverage and then baked-dried with a hot air at 250° C.The conditions thereof are shown in Tables 50 to 53. The thus-producedsteel sheets were evaluated on the aptitude as a fuel tank in the samemanner as in Example 8. The results obtained are shown in Tables 54 to55. TABLE 42 Components of Base Sheet for Plating (wt %) Symbol C Si MnP S Ti Al B N I 0.0012 0.03 0.32 0.007 0.009 0.054 0.04 0.0003 0.0033 II0.0020 0.09 0.32 0.008 0.011 0.040 0.04 — 0.0032

TABLE 43 Precursor of Polyester Polyol Having at Least 3 FunctionalGroups No. Dicarboxylic Acid Glycol Polyol 1001 maleic acid propyleneglycol trimethylolpropane 1002 maleic acid propylene glycol glycerin1003 maleic acid 1,6-hexanediol glycerin 1004 isophthalic acid propyleneglycol trimethylolpropane 1005 isophthalic acid 1,6-hexanediol glycerina maleic acid 1,6-hexanediol none

TABLE 44 Precursor of Blocked Product of Prepolymer Having NCO Group atthe End, Obtained by Reaction of Organic Polyisocyanate or BlockedProduct Thereof with Active Hydrogen Compound No. Compound Having NCOGroup Blocking Agent 1006 tetramethylene diisocyanate phenol 1007tetramethylene diisocyanate isopropyl alcohol 1008 n-xylene diisocyanateisopropyl alcohol

TABLE 45 Epoxy Resin Having at Least One Secondary Hydroxyl Group orAdduct Thereof No. Epoxy Resin Addition Agent 1009 epoxy resin offormula (1) where n is ε-caprolactone 3 on average 1010 epoxy resin offormula (1) where n is ε-caprolactone 8 on average 1011 epoxy resin offormula (1) where n is ethylene oxide 8 on average

TABLE 46 Composition of Organic Resin Constitutional Ratio (equivalentratio) OH Group equivalent of (a)/regenerated NCO group equivalent of(b), or OH group equivalent of (a) + (c)/ Mass (a) (b) (c) regeneratedNCO ratio Precursor Precursor Resin of group equivalent of No. of Table2 of Table 3 Table 4 of (b) (a):(c) Remarks 1012 No. 1001 No. 1006 none1/1 — Invention 1013 No. 1001 No. 1007 none 1/1 — 1014 No. 1001 No. 1008none 1/1 — 1015 No. 1002 No. 1006 none 1.2/1   — 1016 No. 1003 No. 1007none 1.2/1   — 1017 No. 1004 No. 1008 none 0.8/1   — 1018 No. 1005 No.1007 none 0.9/1   — 1019 No. 1001 No. 1006 No. 1009 1/1 7:3 1020 No.1001 No. 1007 No. 1010 1/1 7:3 1021 No. 1005 No. 1006 No. 1010 1/1 6:41022 No. 1005 No. 1007 No. 1009 1/1 6:4 1023 No. 1005 No. 1007 No. 10111/1 6:4 1024 No. 1005 No. 1008 No. 1009 1/1 6:4 A No. a No. 1007 No.1009 1/1 6:4 Comparison B No. a No. 1008 No. 1009 1/1 6:4

TABLE 47 Electrically Conducting Pigment No. Kind 1025 aluminum 1026zinc 1027 nickel 1028 stainless steel 1029 iron phosphide 1030ferrosilicon (Fe: 55%, Si: 45%) 1031 ferrosilicon (Fe: 20%, Si: 80%)1032 a 10/1 (by mol) mixture of ferrosilicon (Fe: 20%, Si: 80%) andstainless steel 1033 silicon

TABLE 48 Rust-Preventive Pigment No. Kind 1034 a 1/1 (by mass) mixtureof magnesium secondary phosphate and baked Mn₂O₃.V₂O₅ 1035 a 1/1 (bymol) mixture of Ca₃(PO₄)₂ and V₂O₅ 1036 strontium chromate 1037magnesium secondary phosphate 1038 baked 2CaO.V₂O₅

TABLE 49 Undercoating Treatment Undercoating Chemicals HexavalentTrivalent No. (component ratio by mass) Chromium Chromium 1039 aqueoussolution of hexavalent chromic acid:fine particulate silica = 50:50 + +1040 aqueous solution of hexavalent chromic acid:fine particulatesilica:etching fluoride = 100:30:10 + + 1041 aqueous solution ofhexavalent chromic + + acid 1042 aqueous solution of trivalent chromicacid − +− 1043 phenol resin:silane coupling agent:phosphoric acid =100:10:10 − − 1044 phenol resin:silane coupling agent:phosphoricacid:silica = 100:10:10:20 − − 1045 acrylolefin:silane couplingagent:silica = 100:10:30 − − 1046 acrylolefin:silane couplingagent:silica:tannic acid = 100:10:30:10 − −+: contained,−: not contained

TABLE 50 Specification (1 of 4) of Coated Metal Material Plating LayerUndercoating Layer Steel Coverage Coverage Sheet Kind (g/m²) Kind(mg/m²) Example 1 I Sn 40 No. 1043 300 Example 2 II Sn—8% Zn 40 No. 1043300 Example 3 I Sn—8% Zn—2% Mg 40 No. 1043 300 Example 4 I Sn—8% Zn—2%Mg—1% Al 40 No. 1043 300 Example 5 I Sn—5% Zn 40 No. 1043 300 Example 6I Sn—20% Zn 40 No. 1043 300 Example 7 I Sn—40% Zn 40 No. 1043 300Example 8 I Sn—8% Zn 20 No. 1043 300 Example 9 I Sn—8% Zn 50 No. 1043300 Example 10 I Sn—8% Zn 40 No. 1043 300 Example 11 I Sn—8% Zn 40 No.1043 300 Example 12 I Sn—8% Zn 40 No. 1043 300 Example 13 I Sn—8% Zn 40No. 1043 300 Example 14 I Sn—8% Zn 40 No. 1043 300 Example 15 I Sn—8% Zn40 No. 1043 300 Example 16 I Sn—8% Zn 40 No. 1043 300 Example 17 I Sn—8%Zn 40 No. 1043 300 Example 18 I Sn—8% Zn 40 No. 1043 300 Example 19 ISn—8% Zn 40 No. 1043 300 Example 20 I Sn—8% Zn 40 No. 1043 300 Example21 I Sn—8% Zn 40 No. 1043 300 Example 22 I Sn—8% Zn 40 No. 1043 300Example 23 I Sn—8% Zn 40 No. 1043 300 Example 24 I Sn—8% Zn 40 No. 1043300 Example 25 I Sn—8% Zn 40 No. 1043 300 Example 26 I Sn—8% Zn 40 No.1043 300 Example 27 I Sn—8% Zn 40 No. 1043 300 Example 28 I Sn—8% Zn 40— — Example 29 I Sn—8% Zn 40 — — Example 30 I Sn—8% Zn 40 — — Example 31I Sn—8% Zn 40 — —

TABLE 51 Specification (2 of 4) of Coated Metal Material Plating LayerUndercoating Layer Cover- Cover- Steel age age Sheet Kind (g/m²) Kind(mg/m²) Example 32 I Sn—8% Zn 40 No. 1039 20 Example 33 I Sn—8% Zn 40No. 1040 20 Example 34 I Sn—8% Zn 40 No. 1041 20 Example 35 I Sn—8% Zn40 No. 1042 20 Example 36 I Sn—8% Zn 40 No. 1044 300 Example 37 I Sn—8%Zn 40 No. 1045 100 Example 38 I Sn—8% Zn 40 No. 1046 100 Example 39 ISn—8% Zn 40 No. 1043 300 Example 40 I Sn—8% Zn 40 No. 1043 300 Example41 I Sn—8% Zn 40 No. 1043 300 Example 42 I Sn—8% Zn 40 No. 1043 300Example 43 I Sn—8% Zn 40 No. 1043 300 Example 44 I Sn—8% Zn 40 No. 1043300 Example 45 I Sn—8% Zn 20 No. 1043 300 Example 46 I Sn—8% Zn 30 No.1043 300 Example 47 I Sn—8% Zn 60 No. 1043 300 Example 48 I Sn—8% Zn 50No. 1043 300 Comparative I Sn 40 No. 1043 300 Example 1 Comparative ISn—8% Zn 40 No. 1043 300 Example 2 Comparative I Sn 40 No. 1043 300Example 3 Comparative I Sn—8% Zn 40 No. 1043 300 Example 4 Comparative ISn—8% Zn 40 No. 1043 300 Example 5 Comparative I Sn—8% Zn 40 No. 1043300 Example 6 Comparative I Sn—8% Zn 40 No. 1043 300 Example 7Comparative I Zn—Ni 40 No. 1043 300 Example 8 electroplating ComparativeI Zn—Ni 40 No. 1043 300 Example 9 electroplating Comparative I alloyedhot-dip 40 No. 1043 300 Example 10 galvanization Comparative Ielectrogalvanization 40 — — Example 11 Comparative I hot-dip 60 — —Example 12 galvanization

TABLE 52 Specification (3 of 4) of Coated Metal Material Composition ofOrganic Film Electrically Rust- Conducting Preventive Organic ResinPigment Pigment Thickness *Coated Kind Vol % Kind Vol % Kind Vol % (μm)Surface Example 1 No. 1012 65 No. 1032 35 — 0 10 both Example 2 No. 101265 No. 1032 35 — 0 10 both Example 3 No. 1012 65 No. 1032 35 — 0 10 bothExample 4 No. 1012 65 No. 1032 35 — 0 10 both Example 5 No. 1012 65 No.1032 35 — 0 10 both Example 6 No. 1012 65 No. 1032 35 — 0 10 bothExample 7 No. 1012 65 No. 1032 35 — 0 10 both Example 8 No. 1013 65 No.1032 35 — 0 10 both Example 9 No. 1014 65 No. 1032 35 — 0 10 bothExample 10 No. 1015 65 No. 1032 35 — 0 10 both Example 11 No. 1016 65No. 1032 35 — 0 10 both Example 12 No. 1017 65 No. 1032 35 — 0 10 bothExample 13 No. 1018 65 No. 1032 35 — 0 10 both Example 14 No. 1019 65No. 1032 15 — 0 10 both Example 15 No. 1020 65 No. 1032 45 — 0 10 bothExample 16 No. 1021 65 No. 1032 15 — 0 10 both Example 17 No. 1022 65No. 1032 45 — 0 10 both Example 18 No. 1023 65 No. 1032 35 — 0 10 bothExample 19 No. 1024 65 No. 1032 35 — 0 10 both Example 20 No. 1019 65No. 1025 35 No. 1034 5 10 both Example 21 No. 1019 65 No. 1026 35 No.1034 5 10 both Example 22 No. 1019 60 No. 1027 35 No. 1034 5 10 bothExample 23 No. 1019 60 No. 1028 35 No. 1034 5 10 both Example 24 No.1019 60 No. 1029 35 No. 1034 5 10 both Example 25 No. 1019 60 No. 103035 No. 1034 5 10 both Example 26 No. 1019 60 No. 1031 35 No. 1034 5 10both Example 27 No. 1019 60 No. 1033 35 No. 1034 5 10 both Example 28No. 1019 60 No. 1032 35 No. 1036 5 10 both Example 29 No. 1019 60 No.1032 35 No. 1036 5 10 both Example 30 No. 1019 60 No. 1032 35 No. 1037 510 both Example 31 No. 1019 60 No. 1032 35 No. 1038 5 10 both*both: both surfaces

TABLE 53 Specification (4 of 4) of Coated Metal Material Composition ofOrganic Film Electrically Rust- Conducting Preventive Organic ResinPigment Pigment Thickness *Coated Kind Vol % Kind Vol % Kind Vol % (μm)Surface Example 32 No. A 60 No. 1032 35 No. 1034 5 10 one Example 33 No.A 60 No. 1032 35 No. 1034 5 10 one Example 34 No. A 60 No. 1032 35 No.1034 5 10 one Example 35 No. B 60 No. 1032 35 No. 1034 5 10 one Example36 No. B 60 No. 1032 35 No. 1034 5 10 one Example 37 No. 1019 60 No.1032 35 — 0 10 one Example 38 No. 1019 60 No. 1032 35 — 0 10 one Example39 No. 1019 60 No. 1032 35 No. 1034 5 1 both Example 40 No. 1019 60 No.1032 35 No. 1034 5 5 both Example 41 No. 1019 60 No. 1032 35 No. 1034 515 both Example 42 No. 10A 60 No. 1032 35 No. 1034 5 10 both Example 43No. 10B 60 No. 1032 35 No. 1034 5 10 both Example 44 epoxy 60 No. 103235 No. 1034 5 10 both Example 45 poly- 60 No. 1032 15 No. 1034 5 10 bothester Example 46 acryl 60 No. 1032 35 No. 1034 5 10 both Example 47acryl- 60 No. 1032 35 No. 1034 5 10 both epoxy Example 48 acryl- 60 No.1032 35 No. 1034 5 10 both urethane Comparative No. 1019 25 No. 1032 70No. 1034 5 10 both Example 1 Comparative No. 1019 25 No. 1032 55 No.1034 20 10 both Example 2 Comparative No. 1019 65 No. 1032 35 — 0 35both Example 3 Comparative No. 1019 65 No. 1032 35 — 0 0.5 both Example4 Comparative poly- 100 — 0 — 0 10 both Example 5 ester Comparativeacryl 100 — 0 — 0 10 both Example 6 Comparative No. 1019 100 — 0 — 0 3both Example 7 Comparative No. 1020 95 — 0 No. 1034 5 20 both Example 8Comparative No. 1021 95 — 0 No. 1034 5 10 both Example 9 Comparative No.1019 65 No. 1032 35 — 0 10 both Example 10 Comparative No. A 65 No. 103235 — 0 10 both Example 11 Comparative No. B 65 No. 1032 35 — 0 10 bothExample 12*one: only outer surface side, both: both surfaces

TABLE 54 Performance Evaluation Results (1 of 2) Outer Surface InnerCorro- Surface sion Re- Corrosion Forma- Spot Seam sistance Resistancebility Weldability Weldability Example 1 3 3 4 4 4 Example 2 4 4 4 4 4Example 3 4 4 4 4 4 Example 4 4 4 4 4 4 Example 5 4 4 4 4 4 Example 6 44 4 4 4 Example 7 4 4 4 4 4 Example 8 3 3 4 4 4 Example 9 4 4 4 4 4Example 10 4 4 4 4 4 Example 11 4 4 4 4 4 Example 12 4 4 4 4 4 Example13 4 4 4 4 4 Example 14 4 4 4 3 3 Example 15 4 4 4 4 4 Example 16 4 4 43 3 Example 17 4 4 4 4 4 Example 18 4 4 4 4 4 Example 19 4 4 4 4 4Example 20 4 4 4 4 4 Example 21 4 4 4 4 4 Example 22 4 4 4 4 4 Example23 4 4 4 4 4 Example 24 4 4 4 4 4 Example 25   4+ 4 4 4 4 Example 26  4+ 4 4 4 4 Example 27   4+ 4 4 4 4 Example 28 4 3 4 4 4 Example 29 4 34 4 4 Example 30 4 3 4 4 4 Example 31 4 3 4 4 4

TABLE 55 Evaluation Results (2 of 2) of Examples of the Invention andComparative Examples Outer Surface Inner Corro- Surface sion Re-Corrosion Forma- Spot Seam sistance Resistance bility WeldabilityWeldability Example 32 4 3 4 4 4 Example 33 4 3 4 4 4 Example 34 4 3 4 44 Example 35 4 3 4 4 4 Example 36 4 4 4 4 4 Example 37 4 3 4 4 4 Example38 4 3 4 4 4 Example 39 3 4 3 4 4 Example 40 3 4 4 4 4 Example 41   4+ 44 3 3 Example 42 3 4 3 4 4 Example 43 3 4 3 4 4 Example 44 3 4 3 4 4Example 45 3 4 3 4 4 Example 46 3 4 3 4 4 Example 47 3 4 3 4 4 Example48 3 4 3 4 4 Comparative 2 3 1 4 4 Example 1 Comparative 2 4 2 4 4Example 2 Comparative   4+ 3 4 2 2 Example 3 Comparative 2 4 1 4 4Example 4 Comparative 2 4 4 1 1 Example 5 Comparative 2 4 4 1 1 Example6 Comparative 2 4 4 1 1 Example 7 Comparative 2 2 4 2 2 Example 8Comparative 2 2 4 1 1 Example 9 Comparative 4 2 4 4 4 Example 10Comparative 1 2 1 4 4 Example 11 Comparative 1 2 1 4 4 Example 12

Evaluation results are as shown in Tables 54 and 55. In Examples of thepresent invention, the score is 3 or higher in all of the corrosionresistance test, the formability test and the weldability test.Depending on the constitution of Examples, higher performances having ascore of 4 are exhibited. Particularly, in the system where the organicfilm is formed by using a raw material film-forming resin containing (a)a polyester polyol having at least three functional groups, (b) ablocked organic polyisocyanate or a blocked product of a prepolymerhaving an NCO group at the end obtained by the reaction of an organicpolyisocyanate with an active hydrogen compound, and (c) an epoxy resinhaving at least one secondary hydroxyl group or an adduct thereof and inthe system using ferrosilicon as the electrically conducting pigment,good outer surface corrosion resistance is exhibited. Even when not anorganic film containing an electrically conducting pigment but only anundercoating film is present on the inner surface side, good propertiesare exhibited.

Comparative Examples 1 to 12 in Table 55 show cases of using a coatedsteel sheet out of the scope of the present invention. In ComparativeExamples 1 and 2 where the amounts of the electrically conductingpigment and rust inhibitor are too large, the formability and in turnthe corrosion resistance are decreased. In Comparative Example 3 wherethe film thickness is too large, the weldability is bad. In ComparativeExample 4 where the film thickness is too small, the formability andcorrosion resistance are bad. In Comparative Examples 5, 6, 7, 8 and 9where an electrically conducting pigment is not contained in the film,the weldability is bad. In Comparative Example 10 where a zinc-basedplating is used, the inner surface corrosion resistance is slightly bad.In Comparative Examples 11 and 12 where a zinc-based plating is used andmoreover, an undercoating film is not formed, the formability is bandand in turn the corrosion resistance is decreased.

These results reveal that, according to the constitutions of the presentinvention, a rust-preventive steel sheet having excellent corrosionresistance as a fuel tank material of automobiles and exhibiting goodproperty in both resistance weldability and press formability can beprovided.

INDUSTRIAL APPLICABILITY

As is apparent from the description in the foregoing pages, thecoated-metal sheet of the present invention containing electricallyconducting particles controlled in the size distribution can be widelyand easily used for parts which are subjected to welding or required tohave an earthing property and used in automobiles, home appliances, OAdevices, civil engineering-building materials and the like. Also, asgood formability and corrosion resistance can be ensured, this metalsheet allows for application in various uses and greatly contributes tovarious industrial fields. According to the constitutions of the presentinvention, a weldable coated metal material excellent in the corrosionresistance of the formed part can be provided. Furthermore, according tothe constitutions of the present invention, a rust-preventive steelsheet having excellent corrosion resistance as a fuel tank material ofautomobiles, and exhibiting good property in both resistance weldabilityand press formability, can be provided.

1. A coated metal material excellent in electric conductivity, corrosionresistance and formability, comprising a metal sheet having formed on atleast one surface thereof a coat layer containing electricallyconducting particles, wherein assuming that the mode value in the numberdistribution for every each particle size of the electrically conductingparticle is Mn, the mode value in the volume distribution for every eachparticle size of the electrically conducting particle is Mv and thethickness of the coat layer is H, H/10≦Mv≦10H 5Mn≦H≦200Mn 12≦Mv/Mn≦50and at the same time, the content of the electrically conductingparticles in the coat layer is from 15 to 60 vol %.
 2. The coated metalmaterial according to claim 1 wherein Mn is 0.05 to 1.5 μm and Mv is 2to 30 μm.
 3. The coated metal material according to claim 2, comprisinga metal sheet having formed on at least one surface thereof a coat layercontaining electrically conducting particles, wherein the mode value inthe number distribution of the electrically conducting particle, Mn, isin a range of 0.05 to 1.0 μm and the total content of the conductingparticles in the coat layer is in a range of 15 to 60 vol %.
 4. Thecoated metal material according to claim 3, wherein the binder of thecoat layer mainly comprises a urethane bond-containing resin.
 5. Thecoated metal material according to claim 4, comprising a metal sheethaving a coat layer containing electrically conducting particles,wherein the binder of the coat layer mainly comprises a urethanebond-containing resin, said urethane bond-containing resin being anorganic resin produced from a raw film-forming resin material comprising(a) a polyester polyol having at least three functional groups and (b) ablocked organic polyisocyanate or a blocked product of a prepolymerhaving an NCO group at the end obtained by the reaction of an organicpolyisocyanate with an activity hydrogen compound.
 6. The coated metalmaterial according to claim 5, wherein said urethane bond-containingresin is an organic resin produced from a raw film-forming resinmaterial comprising (a) a polyester polyol having at least threefunctional groups, (b) a blocked organic polyisocyanate or a blockedproduct of a prepolymer having an NCO group at the end obtained by thereaction of an organic polyisocyanate with an activity hydrogencompound, and (c) an epoxy resin having at least one secondary hydroxylgroup or an adduct thereof.
 7. The coated metal material according toclaim 3, wherein the number of particles at the mode value in the numberdistribution of said electrically conducting particles occupies 5% ormore in the number of all electrically conducting particles.
 8. Thecoated metal material according to claim 3, wherein the volumedistribution for every each particle size of said electricallyconducting particles has a mode value of 2 to 20 μm.
 9. The coated metalmaterial according to claim 8, wherein the coat layer has a thickness Hin a range of 2 to 20 μm.
 10. The coated metal material according toclaim 9, wherein the maximum particle size of the electricallyconducting particles is 35 μm or less.
 11. The coated metal materialaccording to claim 9, wherein the maximum particle size of theelectrically conducting particles is 25 μm or less.
 12. The coated metalmaterial according to claim 3, wherein the electrically conductingparticles comprise (i) a metal and/or (ii) an alloy or compound of atypical metal, transition metal or semimetal element.
 13. The coatedmetal material according to claim 12, wherein one electricallyconducting pigment comprises an alloy or compound containing 40 mass %or more of silicon, or a composite material thereof.
 14. The coatedmetal material according to claim 12, wherein the electricallyconducting particles in the organic layer comprise an alloy or compoundcontaining 50 mass % or more of silicon, or a composite materialthereof.
 15. The coated metal material according to claim 12, whereinthe electrically conducting particles comprise ferrosilicon.
 16. Thecoated metal material according to claim 12, wherein the electricallyconducting particles comprise ferrosilicon containing 70 mass % or moreof silicon.
 17. The coated metal material according to claim 12, whereinthe electrically conducting pigment comprises at least one selected fromthe group consisting of stainless steel, zinc, aluminum, nickel,ferrosilicon and iron phosphide.
 18. The coated metal material accordingto claim 12, wherein the content of the electrically conducting pigmentin the organic layer is in a range of 5 to 50 vol % in terms of thesolid content.
 19. The coated metal material according to claim 12,wherein the organic layer further comprises a rust-preventive pigment.20. The coated metal material according to claim 19, wherein the organiclayer further comprises from 1 to 40 vol %, in terms of the solidcontent, of a rust-preventive pigment and the sum of the electricallyconducting particles and the rust-preventive pigment is from 5 to 70 vol% in terms of the solid content.
 21. The coated metal material accordingto claim 19, wherein the organic layer comprises from 1 to 50 vol % ofelectrically conducting pigment and from 5 to 40 vol % of therust-preventive pigment, and the electrically conducting pigment andrust-preventive pigment account for from 5 to 70 vol % of the entirecoating layer.
 22. The coated metal material according to claim 12,wherein the coat layer comprises 20 vol % or less of the rust-preventivepigment and/or silica.
 23. The coated metal material according to claim12, wherein the binder of the coat layer mainly comprises athermoplastic resin.
 24. The coated metal material according to claim 6,wherein an organic resin layer containing electrically conductingparticles is formed as the coat layer on at least one surface of asurface-treated steel and the surface roughness of said organic layer isfrom 0.3 to 2.5 μm as the average roughness from center line of surfaceroughness, Ra.
 25. The coated metal material according to claim 24,wherein the surface roughness of said organic film is 20 μm or less asthe maximum height, Rmax.
 26. The coated metal material according toclaim 24, wherein the surface texture of said organic film has a peakcount Pc of 200 peaks or less per 10-mm length with a count level of 0.3μm.
 27. The coated metal material according to claim 24, which comprisesan undercoating film between said organic layer and the surface-treatedsheet.
 28. The coated metal material according to claim 27, wherein thecoverage of the undercoating film is from 10 to 1,000 mg/m².
 29. Thecoated metal material according to claim 6, which comprise, in thefollowing order, a coat layer of a tin or tin alloy on surfaces of thestainless steel sheet, a undercoating layer on one side or both sides ofthe stainless steel sheet, with a coverage of the undercoating layerbeing from 10 to 1,000 mg/m², and an organic layer containingelectrically conductive particles on one side or both sides of thestainless steel sheet, with the thickness of the organic layer beingfrom 1.0 to 20 μm.
 30. (canceled)
 31. (canceled)
 32. (canceled) 33.(canceled)
 34. (canceled)